Schedule of Available for Sale Marketable Securities (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities
Available-for-sale marketable securities, Cost	$ 1,000,625	$ 855,786
Available-for-sale marketable securities, Unrealized Gain	4,818	3,689
Available-for-sale marketable securities, Unrealized (Loss)	(867)	(1,515)
Available-for-sale marketable securities, Fair Market Value	1,004,576us-gaap_AvailableForSaleSecurities	857,960us-gaap_AvailableForSaleSecurities
Available-for-sale marketable securities, Fair Market Value of Investment with Unrealized Losses	583,076	241,760
U.S. Treasury Securities
Schedule of Available-for-sale Securities
Available-for-sale marketable securities, Cost	402,197	468,084
Available-for-sale marketable securities, Unrealized Gain	362	94
Available-for-sale marketable securities, Unrealized (Loss)	(405)	(283)
Available-for-sale marketable securities, Fair Market Value	402,154	467,895
Available-for-sale marketable securities, Fair Market Value of Investment with Unrealized Losses	317,771	108,212
U.S. Government Agency Securities
Schedule of Available-for-sale Securities
Available-for-sale marketable securities, Cost	258,452	202,573
Available-for-sale marketable securities, Unrealized Gain	135	75
Available-for-sale marketable securities, Unrealized (Loss)	(85)	(60)
Available-for-sale marketable securities, Fair Market Value	258,502	202,588
Available-for-sale marketable securities, Fair Market Value of Investment with Unrealized Losses	104,642	84,498
Commercial Paper
Schedule of Available-for-sale Securities
Available-for-sale marketable securities, Cost	140,616	105,583
Available-for-sale marketable securities, Unrealized Gain	26	16
Available-for-sale marketable securities, Unrealized (Loss)	(4)	(1)
Available-for-sale marketable securities, Fair Market Value	140,638	105,598
Available-for-sale marketable securities, Fair Market Value of Investment with Unrealized Losses	41,747	7,993
Corporate Debt Securities
Schedule of Available-for-sale Securities
Available-for-sale marketable securities, Cost	139,374	65,747
Available-for-sale marketable securities, Unrealized Gain	2,414	762
Available-for-sale marketable securities, Unrealized (Loss)	(321)	(1,122)
Available-for-sale marketable securities, Fair Market Value	141,467	65,387
Available-for-sale marketable securities, Fair Market Value of Investment with Unrealized Losses	96,998	40,355
Equity And Debt Mutual Funds
Schedule of Available-for-sale Securities
Available-for-sale marketable securities, Cost	10,492	10,463
Available-for-sale marketable securities, Unrealized Gain	1,870	2,742
Available-for-sale marketable securities, Unrealized (Loss)	(29)	(49)
Available-for-sale marketable securities, Fair Market Value	12,333	13,156
Available-for-sale marketable securities, Fair Market Value of Investment with Unrealized Losses	1,234	702
Certificates of Deposit and Time Deposits
Schedule of Available-for-sale Securities
Available-for-sale marketable securities, Cost	49,048	3,258
Available-for-sale marketable securities, Unrealized Gain	11
Available-for-sale marketable securities, Unrealized (Loss)	(23)
Available-for-sale marketable securities, Fair Market Value	49,036	3,258
Available-for-sale marketable securities, Fair Market Value of Investment with Unrealized Losses	20,684
Non-U.S. Government Securities
Schedule of Available-for-sale Securities
Available-for-sale marketable securities, Cost	446	78
Available-for-sale marketable securities, Fair Market Value	$ 446	$ 78

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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