Investments Portfolio of Marketable Securities (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Available-for-sale securities:
Cost	$ 229,948	$ 250,088
Gross Unrealized Gains	15,930	3,184
Gross Unrealized Losses	(5,484)	(2,257)
Estimated Fair Value	240,394	251,015
Cash equivalents cost	(61,909)	(51,887)
Cash equivalents estimated fair value	(61,909)	(51,887)
Marketable securities cost	168,039	198,201
Marketable securities estimated fair value	178,485	199,128
Short-term deposits
Available-for-sale securities:
Cost	60,909	48,596
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	60,909	48,596
Mutual funds
Available-for-sale securities:
Cost	15,722	10,368
Gross Unrealized Gains	5,061	1,452
Gross Unrealized Losses	0	0
Estimated Fair Value	20,783	11,820
United States government securities
Available-for-sale securities:
Cost	50,356	99,299
Gross Unrealized Gains	23	178
Gross Unrealized Losses	0	0
Estimated Fair Value	50,379	99,477
Corporate securities
Available-for-sale securities:
Cost	69,806	20,842
Gross Unrealized Gains	9,961	1,255
Gross Unrealized Losses	(5,208)	(1,980)
Estimated Fair Value	74,559	20,117
Corporate obligations
Available-for-sale securities:
Cost	31,356	48,708
Gross Unrealized Gains	885	283
Gross Unrealized Losses	(276)	(277)
Estimated Fair Value	31,965	48,714
Commercial paper
Available-for-sale securities:
Cost	1,799	22,275
Gross Unrealized Gains	0	16
Gross Unrealized Losses	0	0
Estimated Fair Value	$ 1,799	$ 22,291