Convertible Notes (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Debt Instrument [Line Items]
Convertible notes, short-term	$ 168,658	$ 164,047
Convertible notes, long-term	110,962	109,629
Convertible Senior Notes [Member]
Debt Instrument [Line Items]
Principal amount of convertible notes	310,500	310,500
Unamortized discount	(30,880)	(36,824)
Total convertible notes	279,620	273,676
Convertible notes, short-term	168,658	164,047
Convertible notes, long-term	110,962	109,629
Convertible Senior Notes [Member] | 5% Convertible Senior Notes due 2014
Debt Instrument [Line Items]
Convertible notes stated interest rate (as a percent)	5.00%	5.00%
Principal amount of convertible notes	172,500	172,500
Unamortized discount	(3,842)	(8,453)
Convertible Senior Notes [Member] | 1.125% Convertible Senior Notes due 2018
Debt Instrument [Line Items]
Convertible notes stated interest rate (as a percent)	1.125%	1.125%
Principal amount of convertible notes	138,000	138,000
Unamortized discount	$ (27,038)	$ (28,371)