Income Taxes - Components of Income Tax Expense (Benefit) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
U.S. federal income taxes:
Current	$ 27	$ (17)	$ 22
Deferred	(523)	1,396	1,732
Foreign income taxes:
Current	(379)	(393)	(123)
Deferred	(2,269)	(5,177)	(1,003)
State income taxes:
Deferred	264	314	388
Total income tax expense (benefit)	$ (2,880)	$ (3,877)	$ 1,016