Income Taxes - Current and Deferred Components of Income Tax (Benefit) Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Current income tax expense
Federal	$ 59	$ 5,057
State	113	341
Total current income tax expense	172	5,398
Deferred tax (benefit) expense
Federal	(29,125)	19,534
Foreign		270
State	(66)	(216)
Total deferred income tax (benefit) expense	(29,191)	19,588
Total income tax (benefit) expense	$ (29,019)	$ 24,986