Income Taxes - Deferred Tax Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Tax credits and NOLs	$ 468,612	$ 457,718
Depreciation and amortization	9,631	10,811
Deferred revenue	17,415	27,195
Accruals and reserves	14,103	17,163
Stock-based compensation	62,793	18,956
Derivative liability	0	33,200
Other items	24,834	16,218
Gross deferred tax assets	597,388	581,261
Valuation allowance	(566,442)	(542,409)
Net deferred tax assets	30,946	38,852
Investment in PPA entities	(21,587)	(25,252)
Debt issuance cost	(8,586)	(12,827)
Gross deferred tax liabilities	(30,173)	(38,079)
Deferred tax assets, net	$ 773	$ 773