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Document and Entity Information - USD ($)	3 Months Ended
Document and Entity Information - USD ($)	Mar. 31, 2011	Apr. 30, 2011	Jun. 30, 2010
Document and Entity Information [Abstract]
Entity Registrant Name	MKS INSTRUMENTS INC
Entity Central Index Key	0001049502
Document Type	10-Q
Document Period End Date	Mar. 31, 2011
Amendment Flag	false
Document Fiscal Year Focus	2011
Document Fiscal Period Focus	Q1
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Public Float			$ 938,960,587
Entity Common Stock, Shares Outstanding		52,264,426

Consolidated Balance Sheets (Unaudited) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2011	Dec. 31, 2010
Current assets:
Cash and cash equivalents	$ 259,207	$ 162,476
Short-term investments	219,913	269,457
Trade accounts receivable, net	155,682	138,181
Inventories	159,843	156,429
Deferred income taxes	13,489	13,775
Other current assets	15,440	12,577
Total current assets	823,574	752,895
Property, plant and equipment, net	68,912	68,976
Long-term marketable securities	1,301	0
Goodwill	140,020	140,020
Intangible assets, net	1,493	1,743
Other assets	14,019	18,779
Total assets	1,049,319	982,413
Current liabilities:
Short-term borrowings	1,511	0
Accounts payable	34,856	36,427
Accrued compensation	24,895	29,944
Income taxes payable	13,077	5,347
Other current liabilities	35,713	37,968
Total current liabilities	110,052	109,686
Other liabilities	$ 27,823	$ 25,688
Commitments and contingencies (Note 15)
Stockholders' equity:
Preferred Stock, $0.01 par value, 2,000,000 shares authorized; none issued and outstanding	$ 0	$ 0
Common Stock, no par value, 200,000,000 shares authorized; 52,235,202 and 50,648,601 shares issued and outstanding at March 31, 2011 and December 31, 2010, respectively	113	113
Additional paid-in capital	694,355	663,792
Retained earnings	201,636	171,356
Accumulated other comprehensive income	15,340	11,778
Total stockholders' equity	911,444	847,039
Total liabilities and stockholders' equity	$ 1,049,319	$ 982,413

Consolidated Balance Sheets (Unaudited) (Parenthetical) - $ / shares	Mar. 31, 2011	Dec. 31, 2010
Stockholders' equity:
Preferred Stock, par value	$ 0.01	$ 0.01
Preferred Stock, shares authorized	2,000,000	2,000,000
Preferred Stock, shares issued	0	0
Preferred Stock, shares outstanding	0	0
Common Stock, par value	$ 0	$ 0
Common Stock, shares authorized	200,000,000	200,000,000
Common Stock, shares issued	52,235,202	50,648,601
Common Stock, shares outstanding	52,235,202	50,648,601

Consolidated Statements of Operations (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2011	Mar. 31, 2010
Net revenues:
Products	$ 207,447	$ 171,071
Services	24,404	21,095
Total net revenues	231,851	192,166
Cost of revenues:
Cost of products	111,215	94,139
Cost of services	14,275	12,532
Total cost of revenues	125,490	106,671
Gross profit	106,361	85,495
Research and development	16,896	15,675
Selling, general and administrative	32,707	27,812
Amortization of intangible assets	250	469
Gain on sale of assets		(682)
Income from operations	56,508	42,221
Interest income	276	347
Interest expense	5	22
Income from continuing operations before income taxes	56,779	42,546
Provision for income taxes	18,736	13,548
Income from continuing operations	38,043	28,998
Income from discontinued operations, net of taxes		227
Net income	$ 38,043	$ 29,225
Basic income per share:
Continuing operations	$ 0.74	$ 0.58
Discontinued operations		0.01
Net income	0.74	0.59
Diluted income per share:
Continuing operations	0.73	0.57
Discontinued operations		0.01
Net income	0.73	$ 0.58
Cash dividends paid per common share	$ 0.15
Weighted average common shares outstanding:
Basic	51,407	49,601
Diluted	52,386	50,600

Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2011	Mar. 31, 2010
Cash flows from operating activities:
Net income	$ 38,043	$ 29,225
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	3,177	3,830
Stock-based compensation	3,092	2,137
Provision for excess and obsolete inventory	3,066	1,925
Deferred income taxes	2,993	506
Excess tax benefits from stock-based compensation	(5,032)	(80)
Other	(289)	(797)
Changes in operating assets and liabilities:
Trade accounts receivable	(16,838)	(40,850)
Inventories	(5,984)	(10,907)
Income taxes	12,161	10,570
Other current assets	(1,048)	(145)
Accrued expenses and other current liabilities	(4,847)	10,581
Accounts payable	(1,726)	10,722
Net cash provided by operating activities	26,768	16,717
Cash flows from investing activities:
Purchases of short-term and long-term available-for-sale investments	(103,721)	(73,470)
Maturities, sales and settlements of short-term and long-term available-for-sale investments	152,514	81,808
Purchases of property, plant and equipment	(2,331)	(3,274)
Proceeds from sale of assets	4	2,113
Other	(35)	190
Net cash provided by investing activities	46,431	7,367
Cash flows from financing activities:
Proceeds from short-term borrowings	2,988	39,454
Payments on short-term borrowings	(1,462)	(42,717)
Net proceeds (payments) related to employee stock awards	22,672	(2,593)
Dividend payment to common stockholders	(7,763)
Excess tax benefit from stock-based compensation	5,032	80
Net cash provided by (used in) financing activities	21,467	(5,776)
Effect of exchange rate changes on cash and cash equivalents	2,065	(1,012)
Increase in cash and cash equivalents	96,731	17,296
Cash and cash equivalents at beginning of period	162,476	111,009
Cash and cash equivalents at end of period	$ 259,207	$ 128,305

Basis of Presentation

3 Months Ended

Mar. 31, 2011

Basis of Presentation [Abstract]

Basis of Presentation

The terms “MKS” and the “Company” refer to MKS Instruments, Inc. and its subsidiaries. The interim financial data as of March 31, 2011 and for the three months ended March 31, 2011 and 2010 are unaudited; however, in the opinion of MKS, the interim data includes all adjustments, consisting only of normal recurring adjustments, necessary for a fair statement of the results for the interim periods. The consolidated balance sheet presented as of December 31, 2010 has been derived from the audited consolidated financial statements as of that date. The unaudited consolidated financial statements presented herein have been prepared in accordance with the instructions to Form 10-Q and do not include all of the information and note disclosures required by United States generally accepted accounting principles (“U.S. GAAP”). The consolidated financial statements should be read in conjunction with the audited consolidated financial statements and notes thereto included in the MKS Annual Report on Form 10-K for the year ended December 31, 2010 filed with the Securities and Exchange Commission on February 25, 2011.

The preparation of these consolidated financial statements requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and the disclosure of contingent liabilities at the date of the consolidated financial statements and the reported amounts of revenues and expenses during the reporting period. On an on-going basis, management evaluates its estimates and judgments, including those related to revenue recognition, stock-based compensation, inventory, intangible assets, goodwill and other long-lived assets, acquisition expenses, income taxes and investments. Management bases its estimates and judgments on historical experience and on various other factors that are believed to be reasonable under the circumstances, the results of which form the basis for making judgments about the carrying values of assets and liabilities that are not readily apparent from other sources. Actual results may differ from these estimates under different assumptions or conditions.

- Definition

Description of the basis of accounting used to prepare the financial statements (for example, U.S. Generally Accepted Accounting Principles, Other Comprehensive Basis of Accounting, IFRS). And describes an entity's accounting policy regarding (1) the principles it follows in consolidating or combining the separate financial statements, including the principles followed in determining the inclusion or exclusion of subsidiaries or other entities in the consolidated or combined financial statements and (2) its treatment of interests (for example common stock, a partnership interest or other means of exerting influence) in other entities, for example consolidation or use of the equity or cost methods of accounting. An entity also may describe its accounting treatment for intercompany accounts and transactions, noncontrolling interest, and the income statement treatment in consolidation for issuances of stock by a subsidiary. And provides an entity's explanation that the preparation of financial statements in conformity with generally accepted accounting principles requires the use of management estimates. Estimates used in the determination of carrying amounts of assets or liabilities, or in disclosure of gain or loss contingencies should be disclosed if known information available prior to issuance of the financial statements indicates that both of these criteria are met: (1) It is at least reasonably possible that the estimate of the effect on the financial statements of a condition, situation, or set of circumstances that existed at the date of the financial statements will change in the near term (less than one year from the date of issuance) due to one or more future confirming events, and (2) The effect of the change would be material to the financial statements. The disclosure should indicate the nature of the uncertainty and include an indication that it is at least reasonably possible that a change in the estimate will occur in the near term. Disclosure of the factors that cause the estimate to be sensitive to change also is encouraged. Entities also may identify those areas that are subject to significant estimates. And classifications in the current financial statements may be different from classifications in the prior year's financial statements. Disclose any material changes in classification including an explanation of the reason for the change and the areas impacted.

+ References + Details

Recently Issued Accounting Pronouncements

3 Months Ended

Mar. 31, 2011

Recently Issued Accounting Pronouncements [Abstract]

Recently Issued Accounting Pronouncements

In October 2009, the Financial Accounting Standards Board (“FASB”) issued guidance that establishes new accounting and reporting provisions for arrangements including multiple revenue-generating activities. This guidance provides amendments to the criteria for separating deliverables, measuring and allocating arrangement consideration to one or more units of accounting. The amendments in this guidance also establish a selling price hierarchy for determining the selling price of a deliverable. Significantly enhanced disclosures are also required to provide information about a vendor’s multiple-deliverable revenue arrangements, including information about the nature and terms, significant deliverables, and its performance within arrangements. The amendments also require providing information about the significant judgments made and changes to those judgments and about how the application of the relative selling-price method affects the timing or amount of revenue recognition. The amendments in this guidance are effective prospectively for revenue arrangements entered into or materially modified in the fiscal years beginning on or after June 15, 2010. The Company adopted the new guidance in the first quarter of 2011, and the adoption did not have a material impact on the Company’s financial position, results of operations or cash flows.

In October 2009, the FASB issued guidance that changes the accounting model for revenue arrangements that include both tangible products and software elements that are “essential to the functionality,” and scopes these products out of current software revenue guidance. The new guidance includes factors to help companies determine what software elements are considered “essential to the functionality.” The amendments will now subject software-enabled products to other revenue guidance and disclosure requirements, such as guidance surrounding revenue arrangements with multiple-deliverables. The amendments in this guidance are effective prospectively for revenue arrangements entered into or materially modified in the fiscal years beginning on or after June 15, 2010. The Company adopted the new guidance in the first quarter of 2011, and the adoption did not have a material impact on the Company’s financial position, results of operations or cash flows.

Cash and Cash Equivalents and Investments

3 Months Ended

Mar. 31, 2011

Cash and Cash Equivalents and Investments [Abstract]

Cash and Cash Equivalents and Investments

The fair value of short-term available-for-sale investments with maturities or estimated lives of less than one year consists of the following:


	March 31, 2011		December 31, 2010

Time deposits and drafts	$	1,072	$	15,716
Equity mutual funds		510		491
U.S. agency obligations		218,331		253,250

	$	219,913	$	269,457

The fair value of long-term available-for-sale investments with maturities or estimated lives of more than one year consists of the following:


	March 31, 2011		December 31, 2010

U.S. agency obligations	$	1,301	$	—

The following tables show the gross unrealized gains and (losses) aggregated by investment category:


			Gross		Gross
			Unrealized		Unrealized			Estimated
	Cost		Gains		(Losses)			Fair Value

As of March 31, 2011:
Money market funds	$	19,771	$	—	$	—		$	19,771
Time deposits and drafts		30,107		—		—			30,107
Equity mutual funds		659		—		(149	)		510
U.S. agency obligations		327,554		73		(8	)		327,619

	$	378,091	$	73	$	(157	)	$	378,007


Reported as follows:
Cash and cash equivalents (1)	$	156,791	$	2	$	—		$	156,793
Short-term investments		220,000		70		(157	)		219,913
Long-term marketable securities		1,300		1		—			1,301

	$	378,091	$	73	$	(157	)	$	378,007


			Gross		Gross
			Unrealized		Unrealized			Estimated
	Cost		Gains		(Losses)			Fair Value

As of December 31, 2010:
Money market funds	$	7,032	$	—	$	—		$	7,032
Time deposits and drafts		18,554		—		—			18,554
Equity mutual funds		659		—		(168	)		491
U.S. agency obligations		298,034		42		(35	)		298,041

	$	324,279	$	42	$	(203	)	$	324,118


Reported as follows:
Cash and cash equivalents (1)	$	54,664	$	—	$	(3	)	$	54,661
Short-term investments		269,615		42		(200	)		269,457

	$	324,279	$	42	$	(203	)	$	324,118


(1)		The cash and cash equivalent amounts presented in the tables above do not include cash amounts of $102,414,000 and $107,815,000 as of March 31, 2011 and December 31, 2010, respectively.

Interest income is accrued as earned. Dividend income is recognized as income on the date the stock trades “ex-dividend.” The cost of marketable securities sold is determined by the specific identification method and realized gains or losses are reflected in income and were not material for the three months ended March 31, 2011 and 2010, respectively.

- Definition

The entire cash and cash equivalents footnote disclosure, which may include the types of deposits and money market instruments, applicable carrying amounts, restricted amounts and compensating balance arrangements. Cash and equivalents include: (1) currency on hand (2) demand deposits with banks or financial institutions (3) other kinds of accounts that have the general characteristics of demand deposits (4) short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Generally, only investments maturing within three months from the date of acquisition qualify. This item represents the entire disclosure related to Investments in Certain Debt and Equity Securities (and certain other trading assets) which include all debt and equity securities (other than those equity securities accounted for under the equity or cost methods of accounting) with readily determinable fair values. Other trading assets include assets that are carried on the balance sheet at fair value and held for trading purposes. A debt security represents a creditor relationship with an enterprise that is in the form of a security. Debt securities include, among other items, US Treasury securities, US government securities, municipal securities, corporate bonds, convertible debt, commercial paper, and all securitized debt instruments. An equity security represents an ownership interest in an enterprise or the right to acquire or dispose of an ownership interest in an enterprise at fixed or determinable prices. Equity securities include, among other things, common stock, certain preferred stock, warrant rights, call options, and put options, but do not include convertible debt. An entity may opt to provide the reader with additional narrative text to better understand the nature of investments in debt and equity securities (and other trading assets).

+ References + Details

Fair Value Measurements

3 Months Ended

Mar. 31, 2011

Fair Value Measurements [Abstract]

Fair Value Measurements

In accordance with the provisions of fair value accounting, a fair value measurement assumes that the transaction to sell an asset or transfer a liability occurs in the principal market for the asset or liability or, in the absence of a principal market, the most advantageous market for the asset or liability and defines fair value based upon an exit price model.

The fair value measurement guidance establishes a fair value hierarchy which requires an entity to maximize the use of observable inputs and minimize the use of unobservable inputs when measuring fair value. The guidance describes three levels of inputs that may be used to measure fair value:


Level 1		Quoted prices in active markets for identical assets or liabilities as of the reporting date. Active markets are those in which transactions for the asset or liability occur in sufficient frequency and volume to provide pricing information on an ongoing basis. Level 1 assets and liabilities include money market funds and debt and equity securities.


Level 2		Observable inputs other than Level 1 prices, such as quoted prices for similar assets or liabilities; quoted prices in markets that are not active; or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities. Level 2 assets and liabilities include debt securities with quoted prices that are traded less frequently than exchange-traded instruments and derivative contracts whose value is determined using a pricing model with inputs that are observable in the market or can be derived principally from or corroborated by observable market data. This category generally includes certain time deposits, time drafts and non-exchange traded derivative contracts.


Level 3		Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities. Level 3 assets and liabilities include financial instruments whose value is determined using pricing models, discounted cash flow methodologies, or similar techniques, as well as instruments for which the determination of fair value requires significant management judgment or estimation.

The following tables provide a summary of assets and liabilities of the Company measured at fair value on a recurring basis as of March 31, 2011 and December 31, 2010:


			Fair Value Measurements at Reporting Date Using
			Quoted Prices in Active Markets				Significant
			for Identical		Significant Other		Unobservable
			Assets		Observable		Inputs
Description	March 31, 2011		(Level 1)		Inputs (Level 2)		(Level 3)

Assets:
Available-for-sale securities:
Money market funds	$	19,771	$	19,771	$	—	$	—
Time deposits and drafts		30,107		—		30,107		—
Equity mutual funds		510		510		—		—
U.S. agency obligations		327,619		327,619		—		—
Derivatives — currency forward contracts		343		—		343		—

Total assets	$	378,350	$	347,900	$	30,450	$	—


Liabilities:

Derivatives — currency forward contracts	$	2,746	$	—	$	2,746	$	—


Reported as follows:
Assets:
Cash and cash equivalents	$	156,793	$	127,758	$	29,035	$	—
Short-term investments		219,913		218,841		1,072		—
Long-term marketable securities		1,301		1,301		—		—
Other current assets		343		—		343		—

	$	378,350	$	347,900	$	30,450	$	—

Liabilities:

Other current liabilities	$	2,746	$	—	$	2,746	$	—


			Fair Value Measurements at Reporting Date Using
			Quoted Prices in		Significant		Significant
			Active Markets for		Other		Unobservable
			Identical Assets		Observable		Inputs
Description	December 31, 2010		(Level 1)		Inputs (Level 2)		(Level 3)

Assets:
Available-for-sale securities:
Money market funds	$	7,032	$	7,032	$	—	$	—
Time deposits and drafts		18,554		—		18,554		—
Equity mutual funds		491		491		—		—
U.S. agency obligations		298,041		298,041		—		—
Derivatives — currency forward contracts		369		—		369		—

Total assets	$	324,487	$	305,564	$	18,923	$	—


Liabilities:

Derivatives — currency forward contracts	$	3,463	$	—	$	3,463	$	—


Reported as follows:
Assets:
Cash and cash equivalents	$	54,661	$	51,823	$	2,838	$	—
Short-term investments		269,457		253,741		15,716		—
Other current assets		369		—		369		—

	$	324,487	$	305,564	$	18,923	$	—

Liabilities:

Other current liabilities	$	3,463	$	—	$	3,463	$	—

Money market funds

As of March 31, 2011 and December 31, 2010, this asset class consisted mainly of a money market portfolio that comprises Federal government and U.S. Treasury securities. The asset class is classified within Level 1 of the fair value hierarchy because its underlying investments are valued using quoted market prices in active markets for identical assets.

Time deposits and drafts

As of March 31, 2011, this asset class consisted primarily of time deposits denominated in the Euro currency and time drafts guaranteed by a financial institution. As of December 31, 2010, this asset class consisted of time deposits denominated in the Euro currency. The asset class is valued using other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities and are classified within Level 2 of the fair value hierarchy.

Equity mutual funds

As of March 31, 2011 and December 31, 2010, this asset class consisted of certain U.S. and international equity mutual funds, classified within Level 1 of the fair value hierarchy because they are valued using quoted market prices in an active market for identical assets. The equity mutual funds are associated with the Company’s supplemental defined contribution retirement obligations.

U.S. agency obligations

As of March 31, 2011 and December 31, 2010, this asset class consisted of U.S. agency obligations classified within Level 1 of the fair value hierarchy because they are valued using quoted market prices in an active market for identical assets.

Derivatives

As a result of the Company’s global operating activities, the Company is exposed to market risks from changes in foreign currency exchange rates, which may adversely affect its operating results and financial position. When deemed appropriate, the Company minimizes its risks from foreign currency exchange rate fluctuations through the use of derivative financial instruments. The principal market in which the Company executes its foreign currency contracts is the institutional market in an over-the-counter environment with a relatively high level of price transparency. The market participants usually are large commercial banks. The forward foreign currency exchange contracts are valued using broker quotations, or market transactions and are classified within Level 2 of the fair value hierarchy.

Derivatives

3 Months Ended

Mar. 31, 2011

Derivatives [Abstract]

Derivatives

The Company enters into derivative instruments for risk management purposes only, including derivatives designated as hedging instruments and those utilized as economic hedges. The Company operates internationally and, in the normal course of business, is exposed to fluctuations in interest rates and foreign exchange rates. These fluctuations can increase the costs of financing, investing and operating the business. The Company has used derivative instruments, such as forward contracts, to manage certain foreign currency exposure.

By nature, all financial instruments involve market and credit risks. The Company enters into derivative instruments with major investment grade financial institutions and no collateral is required. The Company has policies to monitor the credit risk of these counterparties. While there can be no assurance, the Company does not anticipate any material non-performance by any of these counterparties.

The Company hedges a portion of its forecasted foreign currency denominated intercompany sales of inventory, over a maximum period of eighteen months, using forward foreign exchange contracts accounted for as cash-flow hedges related to Japanese, South Korean, British and European currencies. To the extent these derivatives are effective in off-setting the variability of the hedged cash flows, and otherwise meet the hedge accounting criteria, changes in the derivatives’ fair value are not included in current earnings but are included in other comprehensive income (“OCI”) in stockholders’ equity. These changes in fair value will subsequently be reclassified into earnings, as applicable, when the forecasted transaction occurs. To the extent that a previously designated hedging transaction is no longer an effective hedge, any ineffectiveness measured in the hedging relationship is recorded currently in earnings in the period it occurs. The cash flows resulting from forward exchange contracts are classified in the consolidated statements of cash flows as part of cash flows from operating activities. The Company does not enter into derivative instruments for trading or speculative purposes.

To the extent the hedge accounting criteria is not met, the related foreign currency forward contracts are considered as economic hedges and changes in the fair value of these contracts are recorded immediately in earnings in the period in which they occur. These include hedges that are used to reduce exchange rate risks arising from the change in fair value of certain foreign currency denominated assets and liabilities (i.e., payables, receivables) and other economic hedges where the hedge accounting criteria were not met.

As of March 31, 2011 and December 31, 2010, the Company had outstanding forward foreign exchange contracts with gross notional values of $75,896,000 and $87,666,000, respectively. The following tables provide a summary of the primary net hedging positions and corresponding fair values held as of March 31, 2011 and December 31, 2010:


	March 31, 2011
	Gross Notional
Currency Hedged (Buy/Sell)	Value		Fair Value (1)

U.S. Dollar/Japanese Yen	$	36,487	$	(1,232	)
U.S. Dollar/South Korean Won		24,225		(956	)
U.S. Dollar/Euro		8,553		(175	)
U.S. Dollar/U.K. Pound Sterling		6,631		(40	)

Total	$	75,896	$	(2,403	)


	December 31, 2010
	Gross Notional
Currency Hedged (Buy/Sell)	Value			Fair Value (1)
U.S. Dollar/Japanese Yen	$	50,104		$	(2,876	)
U.S. Dollar/South Korean Won		27,574			(563	)
U.S. Dollar/Euro		6,934			305
U.S. Dollar/U.K. Pound Sterling		3,054			40

Total	$	87,666		$	(3,094	)


(1) Represents the net receivable (payable) amount included in the consolidated balance sheets.
The following table provides a summary of the fair value amounts of the Company’s derivative instruments:

Derivatives Designated as Hedging Instruments	March 31, 2011			December 31, 2010
Derivative assets:
Forward exchange contracts	$	343		$	369
Derivative liabilities:
Forward exchange contracts		(2,746	)		(3,463	)

Total net derivative liability designated as hedging instruments (1)	$	(2,403	)	$	(3,094	)


(1)		The derivative asset of $343,000 and derivative liability of $2,746,000 are classified in other current assets and other current liabilities, respectively, in the consolidated balance sheet as of March 31, 2011. The derivative asset of $369,000 and derivative liability of $3,463,000 are classified in other current assets and other current liabilities, respectively, in the consolidated balance sheet as of December 31, 2010.

The following table provides a summary of the gains (losses) on derivatives designated as hedging instruments:


	Three Months Ended
Derivatives Designated as Cash Flow Hedging Relationships	March 31,
	2011			2010
Forward exchange contracts:
Net (loss) gain recognized in OCI (1)	$	(162	)	$	481
Net loss reclassified from OCI into income (2)		(526	)		(138	)


(1)		Net change in the fair value of the effective portion classified in OCI.

(2)		Effective portion classified in selling, general and administrative.

Goodwill and Intangible Assets

3 Months Ended

Mar. 31, 2011

Goodwill and Intangible Assets [Abstract]

Goodwill and Intangible Assets

7) Goodwill and Intangible Assets

Goodwill

The Company tests goodwill for impairment on an annual basis, which has been determined to be as of October 31 of each fiscal year. The Company also tests goodwill between annual tests if an event occurs or circumstances change that indicate that the fair value of a reporting unit may be below its carrying value.

Goodwill impairment is determined using a two-step process. The first step involves a comparison of the estimated fair value of a reporting unit to its carrying amount, including goodwill. In performing the first step, the Company determines the fair value of a reporting unit using a discounted cash flow (“DCF”) analysis. Determining fair value requires the exercise of significant judgment, including judgments about appropriate discount rates, perpetual growth rates, and the amount and timing of expected future cash flows. Discount rates are based on a weighted average cost of capital (“WACC”), which represents the average rate a business must pay its providers of debt and equity. The WACC used to test goodwill was derived from a group of comparable companies. The cash flows employed in the DCF analysis were derived from internal earnings and forecasts and external market forecasts. If the estimated fair value of a reporting unit exceeds its carrying amount, goodwill of the reporting unit is not impaired and the second step of the impairment test is not necessary. If the carrying amount of a reporting unit exceeds its estimated fair value, then the second step of the goodwill impairment test must be performed.

The second step of the goodwill impairment test compares the implied fair value of the reporting unit’s goodwill with its carrying amount of goodwill to measure the amount of impairment loss, if any. The implied fair value of goodwill is determined in the same manner as the amount of goodwill recognized in a business combination, whereby the estimated fair value of the reporting unit is allocated to all of the assets and liabilities of that unit (including any unrecognized intangible assets) as if the reporting unit had been acquired in a business combination and the fair value of the reporting unit was the purchase price paid. If the carrying amount of the reporting unit’s goodwill exceeds the implied fair value of that goodwill, an impairment loss is recognized in an amount equal to that excess.

As of October 31, 2010, the Company performed its annual impairment assessment of goodwill and determined that no impairment charges were required, as the fair value of each reporting unit exceeded its book value.

The changes in the carrying amount of goodwill and accumulated impairment losses during the three months ended March 31, 2011 and the twelve months ended December 31, 2010 were as follows:


	2011							2010
	Gross		Accumulated					Gross			Accumulated
	Carrying		Impairment					Carrying			Impairment
	Amount		Loss			Net		Amount			Loss			Net

Beginning balance at January 1	$	279,434	$	(139,414	)	$	140,020	$	337,765		$	(193,254	)	$	144,511
Acquired goodwill (1)		—		—			—		2,292			—			2,292
Sale of discontinued operations (2)		—		—			—		(60,623	)		53,840			(6,783	)

Ending balance at March 31, 2011 and December 31, 2010	$	279,434	$	(139,414	)	$	140,020	$	279,434		$	(139,414	)	$	140,020


(1)		In 2010, the Company purchased a technology company for $2,447,000 to enhance its product portfolio. The Company recorded $2,292,000 of goodwill in connection with the acquisition.

(2)		In 2010, the Company sold its Ion business and assets of its YDI business and as a result charged the related net goodwill to the gain on sale of discontinued operations.

Intangible Assets

Components of the Company’s acquired intangible assets are comprised of the following:


			Accumulated
	Gross		Amortization			Net

As of March 31, 2011:
Completed technology	$	76,829	$	(76,382	)	$	447
Customer relationships		8,940		(8,156	)		784
Patents, trademarks, trade names and other		24,638		(24,376	)		262

	$	110,407	$	(108,914	)	$	1,493


			Accumulated
	Gross		Amortization			Net

As of December 31, 2010
Completed technology	$	76,829	$	(76,230	)	$	599
Customer relationships		8,940		(8,083	)		857
Patents, trademarks, trade names and other		24,638		(24,351	)		287

	$	110,407	$	(108,664	)	$	1,743

Aggregate amortization expense related to acquired intangibles for the three months ended March 31, 2011 and 2010 were $250,000 and $469,000, respectively. Estimated amortization expense for each of the three remaining fiscal years is as follows:


Year	Amount
2011 (remaining)	$	738
2012		389
2013		366

Income Taxes	3 Months Ended
Income Taxes	Mar. 31, 2011
Income Taxes [Abstract]
Income Taxes	10) Income Taxes The Company’s effective tax rate for the three months ended March 31, 2011 and 2010 was 33.0% and 31.8%, respectively. The effective tax rates for the three months ended March 31, 2011 and 2010 and the related income tax provisions were lower than the U.S. statutory tax rate primarily due to geographic mix of income and profits earned by the Company’s international subsidiaries being taxed at rates lower than the U.S. statutory rate. At March 31, 2011, the total amount of gross unrecognized tax benefits, which excludes interest and penalties, was approximately $15,996,000. At December 31, 2010, the total amount of gross unrecognized tax benefits, which excludes interest and penalties, was approximately $15,270,000. The net increase from December 31, 2010 was primarily attributable to an increase in reserves for existing uncertain tax positions. If these benefits were recognized in a future period, the timing of which is not estimable, the net unrecognized tax benefit of $12,789,000, excluding interest and penalties, would impact the Company’s effective tax rate. The Company accrues interest expense and, if applicable, penalties for any uncertain tax positions. Interest and penalties are classified as a component of income tax expense. At March 31, 2011 and December 31, 2010, the Company had accrued interest on unrecognized tax benefits of approximately $1,138,000 and $986,000, respectively. The Company and its subsidiaries are subject to examination by federal, state and foreign tax authorities. The statute of limitations for the Company’s tax filings varies by tax jurisdiction between fiscal years 2001 through present. While the Company believes it has adequately provided for all tax positions, amounts asserted by taxing authorities could materially differ from the Company’s accrued positions as a result of uncertain and complex application of tax regulations. Additionally, the recognition and measurement of certain tax benefits include estimates and judgment by management and inherently includes subjectivity. Accordingly, the Company could record additional provisions or benefits due to U.S. federal, state, and foreign tax-related matters in the future as it revises estimates or settles or otherwise resolves the underlying matters.

Net Income Per Share

3 Months Ended

Mar. 31, 2011

Net Income Per Share [Abstract]

Net Income Per Share

12) Net Income Per Share
The following table sets forth the computation of basic and diluted net income per share:

	Three Months Ended March 31,
	2011		2010
Numerator:
Income from continuing operations	$	38,043	$	28,998
Income from discontinued operations, net of tax		—		227

Net income	$	38,043	$	29,225


Denominator:
Shares used in net income per common share — basic		51,407,000		49,601,000
Effect of dilutive securities:
Stock options, restricted stock and employee stock purchase plan		979,000		999,000

Shares used in net income per common share — diluted		52,386,000		50,600,000


Basic income per common share:
Continuing operations	$	0.74	$	0.58
Discontinued operations		—		0.01

Net income	$	0.74	$	0.59


Diluted income per common share:
Continuing operations	$	0.73	$	0.57
Discontinued operations		—		0.01

Net income	$	0.73	$	0.58

Basic earnings per share (“EPS”) is computed by dividing income available to common stockholders by the weighted-average number of common shares outstanding during the period. The computation of diluted EPS is similar to the computation of basic EPS except that the denominator is increased to include the number of additional common shares that would have been outstanding (using the treasury stock method) if securities containing potentially dilutive common shares (stock options and restricted stock units) had been converted to such common shares, and if such assumed conversion is dilutive.

As of March 31, 2011, stock options and restricted stock units relating to an aggregate of approximately 1,504,968 shares were outstanding. For the three months ended March 31, 2011, 180,292 shares were excluded from the dilutive computation because the exercise price of the options exceeded the average price per share during the period.

As of March 31, 2010, stock options and restricted stock units relating to an aggregate of approximately 3,737,781 shares were outstanding. For the three months ended March 31, 2010, 1,388,643 shares were excluded from the dilutive computation because the exercise price of the options exceeded the average price per share during the period.

Geographic, Product and Significant Customer Information

3 Months Ended

Mar. 31, 2011

Geographic, Product and Significant Customer Information [Abstract]

Geographic, Product and Significant Customer Information

14) Geographic, Product and Significant Customer Information

The Company operates in one segment for the development, manufacturing, sales and servicing of products that measure, control, power and monitor critical parameters of advanced manufacturing processes. The Company’s chief decision-maker reviews consolidated operating results to make decisions about allocating resources and assessing performance for the entire Company.

Information about the Company’s operations in different geographic regions is presented in the tables below. Net revenues to unaffiliated customers are based on the location in which the sale originated. Transfers between geographic areas are at negotiated transfer prices and have been eliminated from consolidated net revenues.


	Three Months Ended March 31,
	2011		2010

Geographic net revenues:
United States	$	110,603	$	112,802
Japan		24,639		30,596
Europe		29,704		20,296
Asia (excluding Japan)		66,905		28,472

	$	231,851	$	192,166


	March 31, 2011		December 31, 2010

Long-lived assets (1):
United States	$	53,155	$	54,840
Japan		4,048		4,273
Europe		5,139		4,970
Asia (excluding Japan)		8,512		8,597

	$	70,854	$	72,680


(1) Long-lived assets include property, plant and equipment, net and certain other assets.
The Company groups its products into three product groups. Net product and service revenues for these product groups are as follows:

	Three Months Ended March 31,
	2011		2010

Instruments and Control Systems	$	112,136	$	89,096
Power and Reactive Gas Products		96,482		85,771
Vacuum Products		23,233		17,299

	$	231,851	$	192,166

Commitments and Contingencies	3 Months Ended
Commitments and Contingencies	Mar. 31, 2011
Commitments and Contingencies [Abstract]
Commitments and Contingencies	15) Commitments and Contingencies Brooks Instrument, LLC filed two lawsuits, in one case along with their affiliate BI Products, LLC (collectively with Brooks Instrument, LLC, “Brooks”), against the Company in the United States District Court for the Eastern District of Texas, on April 29, 2010. Brooks also filed one lawsuit against the Company in the United States District Court for the District of Massachusetts on April 29, 2010. These suits were related to the Company’s digital mass flow controllers and digital pressure sensors. Brooks sought injunctive relief and damages for alleged patent infringement, breach of contract and trade secret violations. None of the lawsuits specified a specific amount of damages. The Company responded to the allegations to deny any wrongdoing. In addition, the Company filed counterclaims against Brooks in the courts where they initially brought suit against the Company, seeking injunctive relief and damages for alleged patent infringement by Brooks, relating to their pressure transient insensitive mass flow controllers. On February 22, 2011, the parties entered into a settlement agreement, resolving all the issues in the cases, and on February 23, 2011, the parties filed stipulated dismissals with the appropriate courts. The Company is subject to various other legal proceedings and claims, which have arisen in the ordinary course of business. In the opinion of management, the ultimate disposition of these matters will not have a material adverse effect on the Company’s results of operations, financial condition or cash flows. The Company reviewed its contractual obligations and commercial commitments as of March 31, 2011 and determined that there were no significant changes from the ones set forth in the notes to the consolidated financial statements included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2010.

Debt	3 Months Ended
Debt	Mar. 31, 2011
Debt [Abstract]
Debt	8) Debt The Company’s Japanese subsidiary has lines of credit and short-term borrowing arrangements with two financial institutions which provide for aggregate borrowings as of March 31, 2011 of up to an equivalent of $30,164,000 U.S. dollars, which generally expire and are renewed at three month intervals. At March 31, 2011 total borrowings outstanding under these arrangements were $1,511,000 at an interest rate of 1.475%. There were no borrowings outstanding at December 31, 2010.