Income Taxes - The differences between the U.S. Federal income taxes computed at the statutory rate (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 22, 2017
Income Tax Expense (Benefit), Continuing Operations, Income Tax Reconciliation [Abstract]
United States statutory rate	21.00%	35.00%	35.00%	35.00%
Statutory federal income tax		$ (11,258)	$ (9,737)	$ (10,530)
Impact of U.S. tax reform		(2,366)	0	0
Change in unrecognized tax benefits		(341)	(2,780)	422
State income tax, less federal benefit		50	9	(6)
Tax difference on foreign earnings		(562)	225	871
Change in foreign taxes		0	0	415
Change in valuation allowance		13,535	8,606	88,737
Tax credits		0	0	(346)
Non-deductible expenses		196	180	359
Other, net		61	101	(17)
Income tax provision (benefit)		(685)	$ (3,396)	$ 79,905
Remeasurement of net deferred tax assets		38,400
Tax benefit for unutilized AMT credits		$ 2,400
Valuation allowance on AMT credit					$ 2,500