Income Taxes - Effective Tax Rate Reconciliation (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Effective income tax rate reconciliation, percent
Federal statutory rate (as a percent)										35.00%	35.00%	35.00%
Effective income tax rate reconciliation
Income tax (benefit) expense computed at statutory rate										$ 6,416	$ 13,155	$ 4,320
State income tax (benefit) expense, net of federal benefit										506	1,201	1,452
Remeasurement of deferred tax assets (lower federal rate)										32,484
Change in valuation allowance on deferred tax assets											(124,525)	(5,336)
Change in state rate										395	688
Share-based compensation costs										470
Other										(3)	(40)
Total income tax expense	$ (38,589)	$ 872	$ (822)	$ (1,729)	$ (438)	$ (38)	$ 110,065	$ (68)		$ 40,268	$ (109,521)	$ 436
Forecast
Effective income tax rate reconciliation, percent
Federal statutory rate (as a percent)									21.00%