Schedule of Available for Sale Marketable Securities (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Schedule of Available-for-sale Securities
Available-for-sale marketable securities, Cost	$ 855,786	$ 663,625
Available-for-sale marketable securities, Unrealized Gain	3,689	3,862
Available-for-sale marketable securities, Unrealized (Loss)	(1,515)	(99)
Available-for-sale marketable securities, Fair Market Value	857,960	667,388
Available-for-sale marketable securities, Fair Market Value of Investments with Unrealized Losses	241,760	59,100
U.S. Treasury Securities
Schedule of Available-for-sale Securities
Available-for-sale marketable securities, Cost	468,084	311,915
Available-for-sale marketable securities, Unrealized Gain	94	216
Available-for-sale marketable securities, Unrealized (Loss)	(283)	(15)
Available-for-sale marketable securities, Fair Market Value	467,895	312,116
Available-for-sale marketable securities, Fair Market Value of Investments with Unrealized Losses	108,212	1,018
U.S. Government Agency Securities
Schedule of Available-for-sale Securities
Available-for-sale marketable securities, Cost	202,573	217,396
Available-for-sale marketable securities, Unrealized Gain	75	262
Available-for-sale marketable securities, Unrealized (Loss)	(60)	(3)
Available-for-sale marketable securities, Fair Market Value	202,588	217,655
Available-for-sale marketable securities, Fair Market Value of Investments with Unrealized Losses	84,498	9,018
Commercial Paper
Schedule of Available-for-sale Securities
Available-for-sale marketable securities, Cost	105,583	70,431
Available-for-sale marketable securities, Unrealized Gain	16	9
Available-for-sale marketable securities, Unrealized (Loss)	(1)	(6)
Available-for-sale marketable securities, Fair Market Value	105,598	70,434
Available-for-sale marketable securities, Fair Market Value of Investments with Unrealized Losses	7,993	25,209
Corporate Debt Securities
Schedule of Available-for-sale Securities
Available-for-sale marketable securities, Cost	65,747	53,405
Available-for-sale marketable securities, Unrealized Gain	762	2,414
Available-for-sale marketable securities, Unrealized (Loss)	(1,122)	(64)
Available-for-sale marketable securities, Fair Market Value	65,387	55,755
Available-for-sale marketable securities, Fair Market Value of Investments with Unrealized Losses	40,355	23,255
Equity And Debt Mutual Funds
Schedule of Available-for-sale Securities
Available-for-sale marketable securities, Cost	10,463	8,767
Available-for-sale marketable securities, Unrealized Gain	2,742	961
Available-for-sale marketable securities, Unrealized (Loss)	(49)	(11)
Available-for-sale marketable securities, Fair Market Value	13,156	9,717
Available-for-sale marketable securities, Fair Market Value of Investments with Unrealized Losses	702	600
Certificates Of Deposit And Time Deposits
Schedule of Available-for-sale Securities
Available-for-sale marketable securities, Cost	3,258	1,627
Available-for-sale marketable securities, Fair Market Value	3,258	1,627
Non-U.S. Government Securities
Schedule of Available-for-sale Securities
Available-for-sale marketable securities, Cost	78	84
Available-for-sale marketable securities, Fair Market Value	$ 78	$ 84