Income Taxes - Reconciliation of Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Effective Income Tax Rate Reconciliation, Amount [Abstract]
U.S. statutory rate	$ (24,136)	$ 1,945	$ (13,556)
Increase (decrease) resulting from:
Permanent differences	330	64	275
State income taxes	(366)	32	0
Vesting of common stock	253	0	0
Other	(274)	0	(88)
Income tax (benefit) expense	$ (24,193)	$ 2,041	$ (13,369)
Effective Income Tax Rate Reconciliation, Percent [Abstract]
U.S. statutory rate	35.00%	35.00%	35.00%
Increase (decrease) resulting from:
Permanent differences	(0.50%)	1.10%	(0.70%)
State income taxes	0.50%	0.60%	0.00%
Vesting of common stock	(0.40%)	0.00%	0.00%
Other	0.50%	0.00%	0.20%
Income tax (benefit) expense	35.10%	36.70%	34.50%