Income Taxes - Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Deferred Tax Assets:
Capitalized research and development	$ 249,371	$ 346,768
Goodwill	26,448	42,082
Capitalized research and development	9,788	11,394
Stock-based compensation	3,924	5,853
Risk management unrealized gain (loss)	1,879	874
Tax credit carryforwards	1,597	1,597
Accrued compensation	1,062	4,419
Inventory capitalization	1,491	3,227
Other	2,945	6,623
Deferred tax assets	298,505	422,837
Deferred Tax Liabilities:
Property, plant and equipment	(27,314)	(61,431)
Convertible debt	(9,889)	(5,797)
Intangibles	(2,195)	(3,591)
Prepaid expenses	(1,393)	(1,724)
Deferred revenue	0	(3,454)
Other	(544)	(2,084)
Deferred tax liabilities	(41,335)	(78,081)
Net deferred tax assets (liabilities)	257,170	344,756
Valuation allowance	(265,362)	(365,035)	$ (250,164)	$ (136,547)
Net deferred tax liabilities	$ (8,192)	$ (20,279)