Income Taxes - Income Tax Expense (Benefit) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Expense (Benefit) [Abstract]
Current federal tax expense (benefit)	$ (41)	$ 227	$ (555)
Deferred federal income tax expense (benefit)	6	3,197	(94)
Federal income tax expense (benefit), continuing operations	(35)	3,424	(649)
Current state and local tax expense (benefit)	36	144	120
Deferred state and local income tax expense (benefit)	0	457	765
State and local income tax expense (benefit), continuing operations	36	601	885
Current foreign tax expense (benefit)	1,857	2,770	295
Deferred foreign income tax expense (benefit)	(762)	(1,248)	(118)
Foreign income tax expense (benefit), continuing operations	1,095	1,522	177
Current income tax expense (benefit)	1,852	3,141	(140)
Deferred income tax expense (benefit)	(756)	2,406	553
Income tax expense	$ 1,096	$ 5,547	$ 413