Investment Securities, Available-for-Sale and Classified as Cash Equivalents (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Investment Securities [Line Items]
Amortized Cost	$ 87,769	$ 56,382
Unrealized Gains	27	5
Unrealized (Losses)	(16)	(5)
Estimated Fair Value	87,780	56,382
U.S. Treasury notes
Investment Securities [Line Items]
Amortized Cost	5,014	2,029
Unrealized Gains		1
Estimated Fair Value	5,014	2,030
Government sponsored enterprise securities
Investment Securities [Line Items]
Amortized Cost	57,470	54,353
Unrealized Gains	12	4
Unrealized (Losses)	(3)	(5)
Estimated Fair Value	57,479	54,352
Commercial paper
Investment Securities [Line Items]
Amortized Cost	13,079
Unrealized Gains	15
Estimated Fair Value	13,094
Corporate debt securities
Investment Securities [Line Items]
Amortized Cost	12,206
Unrealized (Losses)	(13)
Estimated Fair Value	$ 12,193

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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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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