Income Taxes - Net deferred tax assets (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Noncurrent deferred tax assets:
Net operating loss carryforwards	$ 46,056	$ 42,135
Charitable contribution carryforwards	454	410
Research and experimentation credits	1,172	991
Capitalized intangibles	746	741
Stock based compensation	162	158
Depreciation and amortization	2	2
Vacation accrual	28	25
Total noncurrent deferred tax assets	48,620	44,462
Valuation allowance	(48,620)	(44,462)
Net noncurrent deferred tax assets	$ 0	$ 0