Income Taxes - Components of Income Tax Expense (Benefit) Attributable to Current Operations (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Income before income tax expense (benefit)	$ 11,559	$ 22,971	$ 26,298
Current:
Federal tax	199	669	432
State tax	1,006	1,294	622
Foreign tax	270	103	16
Total current	1,475	2,066	1,070
Deferred:
Federal tax	26,348	6,811	(55,716)
State tax	(787)	41	1,020
Foreign tax	(171)	74	(322)
Total deferred	25,390	6,926	(55,018)
Income tax expense (benefit)	$ 26,865	$ 8,992	$ (53,948)