Long-Term Debt (Details) (USD $)	3 Months Ended		0 Months Ended		1 Months Ended	0 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Jun. 30, 2013	Jan. 31, 2013	Jan. 31, 2013	Jul. 15, 2014	Dec. 31, 2014		Apr. 30, 2014
Debt disclosures
Convertible Subordinated Debt, Noncurrent	$ 255,109,000						$ 255,109,000	[1]
Non-recourse notes, due 2029	476,954,000						470,527,000	[1]
Long-term Debt, Excluding Current Maturities	732,063,000						725,636,000
Interest amount added to principal balance	6,427,000	0
Convertible subordinated notes due 2023
Debt disclosures
Convertible Subordinated Debt, Noncurrent	255,109,000						255,109,000
Loan amount				287,500,000	287,500,000
Proceeds from issuances of note payable, net of debt issuance costs				281,200,000
Interest rate (as a percent)				2.125%	2.125%
Conversion rate of shares	48.9758		46.9087		35.9903
Conversion price of convertible notes into common stock (in dollars per share)	$ 20.4200		$ 21.32	$ 27.79	$ 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%
Convertible subordinated notes due 2023 | Common stock
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
Number of common stares received						149,645
Convertible subordinated notes due 2023 | Privately-negotiated capped call option
Debt disclosures
Payments for capped call options				36,800,000	36,800,000
Number of derivative instruments purchased				2	2
Strike price for the underlying number of shares (in dollars per share)	$ 20.4200		$ 21.32	$ 27.79
Cap price for the underlying number of shares (in dollars per share)	27.92		29.16	38.00	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
Convertible subordinated notes due 2023 | Stock prices above $38.00 per share
Debt disclosures
Incremental Common Shares Attributable to Capped Call Options				0
Non-recourse notes payable due 2029
Debt disclosures
Non-recourse notes, due 2029	476,954,000						470,527,000
Non-recourse notes payable due 2029 | GSK
Debt disclosures
Loan amount									450,000,000
Interest rate (as a percent)									9.00%
Percentage of royalties from global net sales									40.00%
Interest amount added to principal balance	6,400,000
Transaction costs									$ 15,300,000

[1] Condensed consolidated balance sheet at December 31, 2014 has been derived from audited consolidated financial statements.