Income Taxes Components of deferred tax asset/ liability (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred tax assets:
Net operating loss carry forwards	$ 62,635	$ 100,378
Tax credit carry forwards	17,078	19,248
Fixed and intangible assets	266	597
Capitalized research and development costs	70	58
Stock based compensation and other reserves and allowances	2,131	3,445
Gross deferred income tax assets	82,180	123,726
Valuation allowance	(82,180)	(123,726)
Net deferred income tax assets	$ 0	$ 0
Percentage of deferred tax assets on which valuation allowance is created	100.00%