Senior Convertible Notes (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Dec. 31, 2013	Jun. 30, 2011
Net carrying amount of the debt component
Senior Convertible Notes	$ 353,269,000		$ 353,269,000		$ 346,060,000
2.75% Senior Convertible Notes due 2017 [Member]
Debt Instrument [Line Items]
Amortization of Debt Discount (Premium)	3,600,000	3,400,000	7,200,000	6,700,000
Contractual Coupon Interest Expense	2,800,000	2,800,000	5,500,000	5,500,000
Net carrying amount of the debt component
Principal amount	402,500,000		402,500,000		402,500,000	402,500,000
Unamortized debt discount	$ (49,231,000)		$ (49,231,000)		$ (56,440,000)