Income Taxes (Current and Deferred Income Tax Expense) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current:
U.S. federal	$ (183)	$ 470	$ 300
Non-U.S.	4,517	7,625	9,142
U.S. state and local	834	201	162
Total current income tax provision (benefit)	5,168	8,296	9,604
Deferred:
U.S. federal	9,950	9,981	(44,068)
Non-U.S.	1,190	334	(3,078)
U.S. state and local	(510)	(900)	(674)
Total deferred income tax provision (benefit)	10,630	9,415	(47,820)
Total:
U.S. federal	9,767	10,451	(43,768)
Non-U.S.	5,707	7,959	6,064
U.S. state and local	324	(699)	(512)
Total income tax provision (benefit)	$ 15,798	$ 17,711	$ (38,216)