Long-Term Debt (Details) (USD $)	12 Months Ended			0 Months Ended	1 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Jul. 15, 2014	Jun. 30, 2013	Jan. 31, 2013
Debt disclosures
Convertible subordinated notes	$ 255,109,000	$ 287,500,000
Total long term debt	725,636,000	287,500,000
Proceeds from issuances of note payable, net of debt issuance costs	434,677,000	281,622,000	(441,000)
Principal amount of debt converted	(32,391,000)	(172,499,000)	0
Convertible Subordinated Notes Due 2023
Debt disclosures
Convertible subordinated notes	255,109,000	287,500,000
Interest rate (as a percent)	2.125%
Loan amount						287,500,000
Proceeds from issuances of note payable, net of debt issuance costs						281,200,000
Conversion rate of shares	48.3294				46.9087	35.9903
Conversion price of convertible notes into common stock (in dollars per share)	$ 20.6913				$ 21.32	$ 27.79
Percentage of principal amount at which the entity may be forced to redeem some or all notes as a result of a fundamental change (as defined)						100.00%
Number of common shares issued upon debt conversion				149,645
Convertible Subordinated Notes Due 2023 | Privately-negotiated capped call option
Debt disclosures
Payments for capped call options						36,800,000
Number of derivative instruments purchased						2
Strike price for the underlying number of shares (in dollars per share)	$ 20.69				$ 21.32	$ 27.79
Cap price for the underlying number of shares (in dollars per share)	28.30				29.16	38.00
Convertible Subordinated Notes Due 2023 | Stock prices below $27.79 per share | Maximum
Debt disclosures
Net shares settlement payable to the entity						2,779,659
Convertible Subordinated Notes Due 2023 | Stock prices below $27.79 per share | Minimum
Debt disclosures
Net shares settlement payable to the entity						0
9% fixed rate term notes due 2029
Debt disclosures
Convertible subordinated notes	$ 470,527,000	$ 0
Common stock | Convertible Subordinated Notes Due 2023
Debt disclosures
Conversion price of convertible notes into common stock (in dollars per share)				21.32
Number of common shares issued upon debt conversion				1,519,402