Marketable Securities Classified as Available-for-Sale (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 183,415	$ 117,861
Gross Unrealized Gain	328	372
Gross Unrealized Loss	(72)	(46)
Fair Value	183,671	118,187
Corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	67,256	49,545
Gross Unrealized Gain	172	203
Gross Unrealized Loss	(25)	(4)
Fair Value	67,403	49,744
Government and agency securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	27,972	23,431
Gross Unrealized Gain	37	43
Gross Unrealized Loss	(28)	(27)
Fair Value	27,981	23,447
Asset-backed securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	33,578	23,079
Gross Unrealized Gain	42	70
Gross Unrealized Loss	(4)
Fair Value	33,616	23,149
Mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	14,481	12,064
Gross Unrealized Gain	56	40
Gross Unrealized Loss	(14)	(15)
Fair Value	14,523	12,089
Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	32,957	1,200
Gross Unrealized Gain	11
Gross Unrealized Loss
Fair Value	32,968	1,200
Municipal bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	6,421	6,273
Gross Unrealized Gain	10	13
Gross Unrealized Loss	(1)
Fair Value	6,430	6,286
Certificates of deposit
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	750	1,003
Gross Unrealized Gain		1
Gross Unrealized Loss
Fair Value	750	1,004
Floating rate notes
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		1,266
Gross Unrealized Gain		2
Gross Unrealized Loss
Fair Value		$ 1,268

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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