Amortized Cost and Fair Value of Investments, with Gross Unrealized Gains and Losses (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 24,043	$ 17,483
Gross Unrealized Gains	11	1
Gross Unrealized Losses		(2)
Fair Value	24,054	17,482
Cash and Cash Equivalents
Schedule of Available-for-sale Securities [Line Items]
Fair Value	5,527	2,768
Marketable securities
Schedule of Available-for-sale Securities [Line Items]
Fair Value	18,322	14,509
Restricted cash
Schedule of Available-for-sale Securities [Line Items]
Fair Value	205	205
Money market funds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	5,733	2,973
Fair Value	5,733	2,973
Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	4,241
Gross Unrealized Gains	7
Fair Value	4,248
Corporate securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	5,263	6,024
Gross Unrealized Gains	1
Gross Unrealized Losses		(2)
Fair Value	5,264	6,022
U.S. government-backed securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	8,304	5,435
Gross Unrealized Gains	3	1
Fair Value	8,307	5,436
U.S. treasury notes
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	502	3,051
Fair Value	$ 502	$ 3,051

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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