Summary of Company's Marketable Securities (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 174,889	$ 190,746
Gross Unrealized Gains	31	78
Gross Unrealized Losses	(97)	(243)
Fair Value	174,823	190,581
Commercial Paper (Due Within 1 Year)
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	22,650	11,397
Gross Unrealized Gains	1
Gross Unrealized Losses	(12)	(2)
Fair Value	22,639	11,395
Corporate Notes (Due Within 1 Year)
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	41,249	51,273
Gross Unrealized Gains	23	19
Gross Unrealized Losses	(4)	(47)
Fair Value	41,268	51,245
Corporate Notes (Due After 1 Year Through 2 Years]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	50,322	53,592
Gross Unrealized Gains	5	50
Gross Unrealized Losses	(72)	(48)
Fair Value	50,255	53,594
U.S. Government Obligations (Due Within 1 Year)
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	7,500	13,532
Gross Unrealized Gains		2
Fair Value	7,500	13,534
U.S. Government Obligations (Due After 1 Year Through 2 Years)
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	53,168	60,202
Gross Unrealized Gains	2	7
Gross Unrealized Losses	(9)	(21)
Fair Value	53,161	60,188
Equity Securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		750
Gross Unrealized Gains	26,300
Gross Unrealized Losses		(125)
Fair Value		$ 625

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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