Income Taxes - Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Deferred Tax Assets:
Capitalized research and development	$ 348,734	$ 278,867
Goodwill	17,028	20,067
Capitalized research and development	0	8,650
Stock-based compensation	3,805	3,447
Interest expense carryforward	4,877	2,940
Tax credit carryforwards	4,330	1,597
Leases	11,364	0
Intangibles	1,530	0
Risk management unrealized loss	131	0
Accrued compensation	4,285	3,318
Inventory capitalization	2,442	1,921
Other	4,589	3,133
Deferred tax assets	403,115	323,940
Deferred Tax Liabilities:
Property, plant and equipment	(41,769)	(38,324)
Leases	(9,459)	0
Convertible debt	(5,213)	(5,648)
Risk management unrealized gain	0	(2,649)
Intangibles	0	949
Prepaid expenses	(2,106)	(1,688)
Deferred revenue	0	(583)
Other	(1,086)	(773)
Deferred tax liabilities	(59,633)	(48,716)
Net deferred tax assets	343,482	275,224
Valuation allowance	(350,457)	(283,634)	$ (265,362)	$ (365,035)
Net deferred tax liabilities	$ (6,975)	$ (8,410)