Income Taxes - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Operating Loss Carryforwards [Line Items]
Statutory income tax rate	21.00%	35.00%	35.00%
Tax depreciation benefit	$ 57,900
Income tax provision on operating loss carryforwards adjustment	6,000
Income tax adjustment	300
Rate change - decrease in valuation allowance	336,417	$ 336,087
Change in valuation allowance	329	71,782
Increase (decrease) in valuation allowance before consideration of the Tax Act	0	48,531
Gross unrecognized tax benefits	18,500	18,500
Penalties and interest accrued	100	100
State
Operating Loss Carryforwards [Line Items]
Valuation allowance adjustment	6,000
Federal
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	1,200,000	1,200,000
Operating loss carryforwards, indefinite lived	33,500
Tax credit valuation allowance	207		$ 13,931
Federal and state
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards valuation allowance	245,300	286,600
Tax credit valuation allowance	49,800	49,500
Change in valuation allowance	(5,919)	$ 294,568	$ 128,931
Capital loss carryforward | Federal
Operating Loss Carryforwards [Line Items]
Tax credit carryforward	165,000
Capital loss carryforward | Federal and state
Operating Loss Carryforwards [Line Items]
Tax credit valuation allowance	$ 41,400