Summary of Investments by Investment Category (Detail) (USD $) In Thousands, unless otherwise specified	6 Months Ended	12 Months Ended
Jun. 30, 2012	Dec. 31, 2011
Cash And Cash Equivalents And Investments
Total investments, Amortized Cost	$ 52,129	$ 61,652
Total investments, Gross Unrealized Gains	167	150
Total investments, Gross Unrealized Losses	(40)	(196)
Total investments, Fair Value	52,256	61,606
US Treasury Securities
Cash And Cash Equivalents And Investments
Available-for-sale securities, Amortized Cost	10,998	6,920
Available-for-sale securities, Gross Unrealized Gains	1	1
Available-for-sale securities, Fair Value	10,999	6,921
U.S. Agency Securities
Cash And Cash Equivalents And Investments
Available-for-sale securities, Amortized Cost	3,508	5,526
Available-for-sale securities, Gross Unrealized Gains	9	25
Available-for-sale securities, Fair Value	3,517	5,551
Corporate notes/bonds
Cash And Cash Equivalents And Investments
Available-for-sale securities, Amortized Cost	36,566	47,600
Available-for-sale securities, Gross Unrealized Gains	157	124
Available-for-sale securities, Gross Unrealized Losses	(40)	(196)
Available-for-sale securities, Fair Value	36,683	47,528
Certificates/Term Deposits
Cash And Cash Equivalents And Investments
Available-for-sale securities, Amortized Cost	1,057	1,606
Available-for-sale securities, Fair Value	$ 1,057	$ 1,606

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.

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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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- 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.

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- Definition

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