Schedule of Available for Sale Marketable Securities (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities
Available-for-sale marketable securities, Cost	$ 745,498	$ 1,000,625
Available-for-sale marketable securities, Unrealized Gain	2,145	4,818
Available-for-sale marketable securities, Unrealized (Loss)	(4,019)	(867)
Available-for-sale marketable securities, Fair Market Value	743,624	1,004,576
Available-for-sale marketable securities, Fair Market Value of Investments with Unrealized Losses	601,660	583,076
U.S. Treasury Securities
Schedule of Available-for-sale Securities
Available-for-sale marketable securities, Cost	421,060	402,197
Available-for-sale marketable securities, Unrealized Gain	65	362
Available-for-sale marketable securities, Unrealized (Loss)	(1,167)	(405)
Available-for-sale marketable securities, Fair Market Value	419,958	402,154
Available-for-sale marketable securities, Fair Market Value of Investments with Unrealized Losses	379,434	317,771
U.S. Government Agency Securities
Schedule of Available-for-sale Securities
Available-for-sale marketable securities, Cost	84,032	258,452
Available-for-sale marketable securities, Unrealized Gain	42	135
Available-for-sale marketable securities, Unrealized (Loss)	(122)	(85)
Available-for-sale marketable securities, Fair Market Value	83,952	258,502
Available-for-sale marketable securities, Fair Market Value of Investments with Unrealized Losses	55,120	104,642
Corporate Debt Securities
Schedule of Available-for-sale Securities
Available-for-sale marketable securities, Cost	163,297	139,374
Available-for-sale marketable securities, Unrealized Gain	902	2,414
Available-for-sale marketable securities, Unrealized (Loss)	(2,565)	(321)
Available-for-sale marketable securities, Fair Market Value	161,634	141,467
Available-for-sale marketable securities, Fair Market Value of Investments with Unrealized Losses	145,373	96,998
Commercial Paper
Schedule of Available-for-sale Securities
Available-for-sale marketable securities, Cost	20,298	140,616
Available-for-sale marketable securities, Unrealized Gain	11	26
Available-for-sale marketable securities, Unrealized (Loss)	(1)	(4)
Available-for-sale marketable securities, Fair Market Value	20,308	140,638
Available-for-sale marketable securities, Fair Market Value of Investments with Unrealized Losses	8,646	41,747
Certificates of Deposit and Time Deposits
Schedule of Available-for-sale Securities
Available-for-sale marketable securities, Cost	43,391	49,048
Available-for-sale marketable securities, Unrealized Gain	6	11
Available-for-sale marketable securities, Unrealized (Loss)	(3)	(23)
Available-for-sale marketable securities, Fair Market Value	43,394	49,036
Available-for-sale marketable securities, Fair Market Value of Investments with Unrealized Losses	10,527	20,684
Equity And Debt Mutual Funds
Schedule of Available-for-sale Securities
Available-for-sale marketable securities, Cost	12,996	10,492
Available-for-sale marketable securities, Unrealized Gain	1,119	1,870
Available-for-sale marketable securities, Unrealized (Loss)	(161)	(29)
Available-for-sale marketable securities, Fair Market Value	13,954	12,333
Available-for-sale marketable securities, Fair Market Value of Investments with Unrealized Losses	2,560	1,234
Non-U.S. Government Securities
Schedule of Available-for-sale Securities
Available-for-sale marketable securities, Cost	424	446
Available-for-sale marketable securities, Fair Market Value	$ 424	$ 446

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

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