Income Taxes - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Operating Loss Carryforwards [Line Items]
Statutory income tax rate	35.00%
Income tax benefit	$ 114,716
Income tax adjustment	(71,800)
Rate change - decrease in valuation allowance	336,087	$ 264,305
Gross unrecognized tax benefits	18,500	29,100
Penalties and interest accrued	100
Federal
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	1,200,000	1,000,000
Federal and state
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards valuation allowance	286,600	218,100
Tax credit valuation allowance	$ 49,500	$ 49,600