Fair Value Measurements (Details 2) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Marketable securities classified as available-for-sale
Amortized Cost	$ 56,863	$ 67,635
Unrealized Gains	27	24
Unrealized Loss	(29)	(54)
Estimated Fair Value	56,861	67,605
U.S. Treasury securities
Marketable securities classified as available-for-sale
Amortized Cost	1,290
Unrealized Gains	1
Estimated Fair Value	1,291
Debt securities of U.S. government-sponsored entities
Marketable securities classified as available-for-sale
Amortized Cost	773	19,351
Unrealized Gains		2
Unrealized Loss		(2)
Estimated Fair Value	773	19,351
Commercial paper
Marketable securities classified as available-for-sale
Amortized Cost	17,974	19,232
Unrealized Gains	20	17
Estimated Fair Value	17,994	19,249
Corporate debt securities
Marketable securities classified as available-for-sale
Amortized Cost	36,826	29,052
Unrealized Gains	6	5
Unrealized Loss	(29)	(52)
Estimated Fair Value	$ 36,803	$ 29,005

This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

+ References+ Details

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.

+ References+ Details

- Definition

This item represents the gross unrealized gains for securities, at a point in time, which are categorized neither as held-to-maturity nor trading securities.

+ References+ Details