Long-Term Debt (Details) $ / shares in Units, $ in Thousands				1 Months Ended	3 Months Ended		6 Months Ended		15 Months Ended
	Jul. 15, 2014 $ / shares shares	Jun. 30, 2014 $ / shares $ / item	Jan. 31, 2013 USD ($) item $ / shares $ / item shares	Jan. 31, 2013 USD ($) item $ / shares $ / item	Jun. 30, 2015 USD ($) $ / shares $ / item	Jun. 30, 2014 USD ($) $ / shares $ / item	Jun. 30, 2015 USD ($) $ / shares $ / item	Jun. 30, 2014 USD ($) $ / shares $ / item	Jun. 30, 2015 USD ($) $ / shares $ / item	Dec. 31, 2014 USD ($)		Apr. 30, 2014 USD ($)
Debt disclosures
Convertible Subordinated Debt, Noncurrent					$ 255,109		$ 255,109		$ 255,109	$ 255,109	[1]
Non-recourse notes, due 2029					483,363		483,363		483,363	470,527	[1]
Long-term Debt, Excluding Current Maturities					738,472		738,472		738,472	725,636
Proceeds from issuances of note payable, net of debt issuance costs							0	$ 434,677
Interest amount added to principal balance							12,836	$ 0
Convertible subordinated notes due 2023
Debt disclosures
Convertible Subordinated Debt, Noncurrent					$ 255,109		$ 255,109		$ 255,109	255,109
Loan amount			$ 287,500	$ 287,500
Proceeds from issuances of note payable, net of debt issuance costs			$ 281,200
Interest rate (as a percent)			2.125%	2.125%
Conversion rate of shares		46.9087		35.9903			49.6963
Conversion price of convertible notes into common stock (in dollars per share) | $ / shares		$ 21.32	$ 27.79	$ 27.79	$ 20.12	$ 21.32	$ 20.12	$ 21.32	$ 20.12
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) | $ / shares	$ 21.32
Number of common shares issued upon debt conversion | shares	1,519,402
Number of common stares received | shares	149,645
Convertible subordinated notes due 2023 | Privately-negotiated capped call option
Debt disclosures
Payments for capped call options			$ 36,800
Number of derivative instruments purchased | item			2	2
Strike price for the underlying number of shares (in dollars per share) | $ / shares		$ 21.32	$ 27.79				$ 20.12
Cap price for the underlying number of shares (in dollars per share) | $ / item		29.16	38.00	38.00	27.52	29.16	27.52	29.16	27.52
Convertible subordinated notes due 2023 | Stock prices below $27.79 per share | Maximum
Debt disclosures
Net shares settlement payable to the entity | shares			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 | shares			0
Convertible subordinated notes due 2023 | Stock prices above $38.00 per share
Debt disclosures
Incremental Common Shares Attributable to Capped Call Options | shares			0
Non-recourse notes payable due 2029
Debt disclosures
Non-recourse notes, due 2029					$ 483,363		$ 483,363		$ 483,363	$ 470,527
Non-recourse notes payable due 2029 | GSK
Debt disclosures
Loan amount												$ 450,000
Interest rate (as a percent)												9.00%
Percentage of royalties from global net sales												40.00%
Interest amount added to principal balance					$ 6,400	$ 0	$ 12,800	$ 0	$ 33,400
Debt issuance costs												$ 15,300

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