Income Taxes - Components of Income Tax (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current income tax expense (benefit)
State	$ 683	$ 896	$ 350
Foreign	96	255	(163)
Total current income tax expense	779	1,151	187
Deferred tax expense (benefit)
Federal	(14,813)	13,195	6,402
State	1,063	2,677	1,377
Foreign	(56)	(41)	(42)
Total deferred income tax expense (benefit)	(13,806)	15,831	7,737
Total income tax expense (benefit)	$ (13,027)	$ 16,982	$ 7,924