Income Taxes - Reconciliation of Expected Income Tax Expense (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
Reconciliation of the expected income tax expense on income (loss) before income taxes using the statutory federal income tax
Expected income tax expense at 35%									$ (10,274)	$ (21,107)	$ (7,389)
Foreign tax rate differential									(2,914)	5,932	1,769
Foreign tax differences									(5,610)	(4,828)	4,104
State and local taxes									116	28	41
Nondeductible expenses									4,308	(259)	578
Change in U.S. tax rate									77,410	0	0
Expired Capital Loss									1,114	1,321	15,950
Valuation allowance:
Valuation allowance on expiring capital losses									(1,114)	(1,321)	(15,950)
Valuation allowance on operations									(63,012)	24,655	4,941
Total income tax expense	$ (3,646)	$ 1,686	$ 2,402	$ (418)	$ (1,444)	$ 3,316	$ 2,256	$ 293	$ 24	$ 4,421	$ 4,044