Income Taxes - Sources of Income (Loss) Before Taxes and Components of Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Sources of income (loss) before income taxes
Domestic									$ (12,487)	$ (41,246)	$ 21,065
Foreign									(16,866)	(19,060)	(42,175)
Loss before income taxes									(29,353)	(60,306)	(21,110)
Current:
Federal									(166)	0	(4,715)
State and local									116	28	41
Foreign									5,494	5,574	1,274
Deferred:
Federal									(1,263)	0	2,726
Foreign									(4,157)	(1,181)	4,718
Total income tax expense	$ (3,646)	$ 1,686	$ 2,402	$ (418)	$ (1,444)	$ 3,316	$ 2,256	$ 293	$ 24	$ 4,421	$ 4,044