Income taxes (Deferred Tax Assets) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Deferred tax assets
Reserves	$ 1,152	$ 1,561
Net operating loss carryforwards	83,608	82,210
R&D credit carryforwards	8,593	7,435
Depreciation/amortization deferred	15,884	13,005
Other	6,076	5,944
Net deferred taxes before valuation allowance	115,313	110,155
Less: Valuation allowance	(115,313)	(110,155)
Deferred tax assets	$ 0	$ 0