Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income taxes
Tax impact of revaluation of deferred tax assets under the TCJA	$ 16,100
Reduction in valuation allowance under the TCJA	16,100
Loss before income taxes
U.S. operations	7,855	$ 8,347	$ 28,643
Foreign operations	28,871	10,551
Loss before income taxes	36,726	18,898	$ 28,643
Net operating loss carry forwards available to offset future federal and state taxable income	131,600	128,100
Proceeds from sale of research and development tax credits		400
Gross deferred tax assets:
Net operating loss carryforwards	36,383	35,559
Accrued expenses	52	52
Contributions	3	4
Deferred expenses		35
Stock-based compensation	1,640	1,459
Research and development and other credits	6,545	5,536
Total gross deferred tax assets	44,623	42,645
Gross deferred tax liabilities:
Depreciation	(18)	(17)
Total gross deferred tax liabilities	(18)	(17)
Net deferred tax assets	44,605	42,628
Less: valuation allowance	(44,605)	(42,628)
Net deferred tax assets after valuation allowance	0	0
Increase (decrease) in valuation allowance	$ 2,000	$ (12,900)
Reconciliation of income tax expense (benefit) at the statutory federal income tax rate and income taxes
Federal income tax expense at statutory rate (as a percent)	21.00%	34.00%	34.00%
Permanent items (as a percent)	(0.90%)	(0.60%)	(1.20%)
State income tax, net of federal benefit (as a percent)	0.10%	2.80%	7.50%
R&D tax credits (as a percent)	4.30%	1.10%	5.20%
Change in federal statutory rate on deferreds (as a percent)	(1.10%)	(85.60%)
Foreign income tax effect (as a percent)	(16.50%)	(19.00%)
Other (as a percent)	(1.60%)	(1.10%)	1.60%
Change in valuation allowance (as a percent)	(5.30%)	68.40%	(47.10%)
Effective income tax rate (as a percent)	0.00%	0.00%	0.00%
Research tax credit carryforward | Federal
Loss before income taxes
Tax credit carryovers	$ 5,700
Research tax credit carryforward | State
Loss before income taxes
Tax credit carryovers	$ 400