Cash Equivalents and Investments Classified as Available-for-sale Securities (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2014	Dec. 31, 2013
Schedule Of Available For Sale Securities [Line Items]
Cost	$ 279,826	$ 315,000
Unrealized Gain	83	85
Unrealized (Loss)	(56)	(28)
Estimated Fair Value	279,853	315,057
Money market funds
Schedule Of Available For Sale Securities [Line Items]
Cost	25,344	57,296
Estimated Fair Value	25,344	57,296
Corporate notes and commercial paper
Schedule Of Available For Sale Securities [Line Items]
Cost	176,466	182,426
Unrealized Gain	54	62
Unrealized (Loss)	(42)	(16)
Estimated Fair Value	176,478	182,472
U.S. government agency securities
Schedule Of Available For Sale Securities [Line Items]
Cost	78,016	75,278
Unrealized Gain	29	23
Unrealized (Loss)	(14)	(12)
Estimated Fair Value	78,031	75,289
Cash equivalents
Schedule Of Available For Sale Securities [Line Items]
Estimated Fair Value	37,151	113,794
Short-term investments
Schedule Of Available For Sale Securities [Line Items]
Estimated Fair Value	198,433	150,892
Long-term investments
Schedule Of Available For Sale Securities [Line Items]
Estimated Fair Value	$ 44,269	$ 50,371