Summary of Unrealized Gains and Losses Related to Cash Equivalents and Investments in Marketable Securities (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	$ 48,319	$ 64,246
Gross Unrealized Gains	54	67
Gross Unrealized Losses	(6)	(1)
Fair Value	48,367	64,312
Cash and Cash Equivalents \| Money Market Funds
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	11	11
Gross Unrealized Gains
Gross Unrealized Losses
Fair Value	11	11
Short-term Investments
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	48,308	64,235
Gross Unrealized Gains	54	67
Gross Unrealized Losses	(6)	(1)
Fair Value	48,356	64,301
Short-term Investments \| Money Market Funds
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	4,858	7,259
Gross Unrealized Gains
Gross Unrealized Losses
Fair Value	4,858	7,259
Short-term Investments \| Corporate Bond Securities
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	27,411	23,151
Gross Unrealized Gains	49	43
Gross Unrealized Losses	(6)	(1)
Fair Value	27,454	23,193
Short-term Investments \| U.S. Federal Agencies
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	14,138	27,241
Gross Unrealized Gains	5	10
Gross Unrealized Losses
Fair Value	14,143	27,251
Short-term Investments \| Foreign Bonds and Notes
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost		4,682
Gross Unrealized Gains		14
Gross Unrealized Losses
Fair Value		4,696
Short-term Investments \| Municipal Obligations
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	1,901	1,902
Gross Unrealized Gains
Gross Unrealized Losses
Fair Value	$ 1,901	$ 1,902

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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