Income taxes (Deferred Tax Assets) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred tax assets
Reserves	$ 1,561	$ 2,351
Net operating loss carryforwards	82,210	126,335
R&D credit carryforwards	7,435	6,998
Depreciation/amortization deferred	13,005	20,024
Deferred revenue	1,081	2,091
Other	5,944	9,045
Net deferred taxes before valuation allowance	111,236	166,844
Less: Valuation allowance	(111,236)	(166,844)
Deferred tax assets	$ 0	$ 0