Income taxes (Deferred Tax Assets) (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Deferred tax assets, current
Reserves	$ 2,351	$ 2,581
Other	910	749
Total gross deferred tax assets, current	3,261	3,330
Deferred tax assets, noncurrent
Net operating loss carryforwards	126,335	122,281
R&D credit carryforwards	6,998	6,747
Depreciation/amortization deferred	20,024	20,848
Deferred revenue	2,091	0
Other	8,135	7,954
Total gross deferred tax assets, noncurrent	163,583	157,830
Net deferred taxes before valuation allowance	166,844	161,160
Less: Valuation allowance	(166,844)	(161,160)
Deferred tax assets	$ 0	$ 0