Schedule of Carrying Amounts and Fair Values of Financial Instruments (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011	Dec. 31, 2010	Mar. 31, 2009
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Cash and cash equivalents, Carrying Value	$ 341,638		$ 338,920		$ 573,736	$ 397,737
Convertible debt, Carrying Value	185,708		169,896
Japan loan, Carrying Value							10,000
Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Cash and cash equivalents, Carrying Value	341,638		338,920
Marketable securities, Carrying Value	857,960		667,388
Convertible debt, Carrying Value	185,708	[1]	169,896	[1]
Japan loan, Carrying Value	955		3,491
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Cash and cash equivalents, Fair Value	341,638		338,920
Marketable securities, Fair Value	857,960		667,388
Convertible debt, Fair Value	611,433	[1]	589,000	[1]
Japan loan, Fair Value	$ 955		$ 3,491

[1] The carrying value represents the bifurcated debt component only, while the fair value is based on quoted market prices for the convertible note which includes the equity conversion feature.