Senior Convertible Notes (Details) (USD $)	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013	Jun. 30, 2011
Net carrying amount of the debt component
Senior Convertible Notes	$ 349,632,000		$ 346,060,000
2.75% Senior Convertible Notes due 2017 [Member]
Debt Instrument [Line Items]
Amortization of Debt Discount (Premium)	3,600,000	3,300,000
Contractual Coupon Interest Expense	2,800,000	2,800,000
Net carrying amount of the debt component
Principal amount	402,500,000		402,500,000	402,500,000
Unamortized debt discount	$ (52,868,000)		$ (56,440,000)