Fair Value Measurements (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Valuation of the company's assets measured at fair value
Money market funds	$ 111,256	$ 96,661
Securities available-for-sale	78,110	72,552
Foreign currency forward contract	155	(337)
Assets Fair Value Total	189,521	168,876
Level 1 [Member]
Valuation of the company's assets measured at fair value
Money market funds	111,256	96,661
Assets Fair Value Total	111,256	96,661
Level 2 [Member]
Valuation of the company's assets measured at fair value
Foreign currency forward contract	155	(337)
Assets Fair Value Total	78,265	72,215
Level 3 [Member]
Valuation of the company's assets measured at fair value
Money market funds
Foreign currency forward contract
Assets Fair Value Total
U.S. government obligations [Member]
Valuation of the company's assets measured at fair value
Securities available-for-sale	55,460	41,351
U.S. government obligations [Member] \| Level 2 [Member]
Valuation of the company's assets measured at fair value
Securities available-for-sale	55,460	41,351
U.S. government obligations [Member] \| Level 3 [Member]
Valuation of the company's assets measured at fair value
Securities available-for-sale
Municipal securities [Member]
Valuation of the company's assets measured at fair value
Securities available-for-sale	20,612	29,145
Municipal securities [Member] \| Level 2 [Member]
Valuation of the company's assets measured at fair value
Securities available-for-sale	20,612	29,145
Municipal securities [Member] \| Level 3 [Member]
Valuation of the company's assets measured at fair value
Securities available-for-sale
Corporate bonds [Member]
Valuation of the company's assets measured at fair value
Securities available-for-sale	2,038	2,056
Corporate bonds [Member] \| Level 2 [Member]
Valuation of the company's assets measured at fair value
Securities available-for-sale	2,038	2,056
Corporate bonds [Member] \| Level 3 [Member]
Valuation of the company's assets measured at fair value
Securities available-for-sale

- Definition

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents Available-for-sale Securities which consist of all investments in certain debt and equity securities neither classified as trading or held-to-maturity securities. A debt security represents a creditor relationship with an enterprise. 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 which are categorized as Available-for-sale.

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