Income Taxes - Net deferred tax assets (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Net operating loss carryforwards	$ 51,758	$ 46,056
Charitable contribution carryforwards	552	454
Research and experimentation credits	1,440	1,172
Capitalized intangibles	781	746
Stock based compensation	193	162
Depreciation and amortization	6	2
Vacation accrual	35	28
Other	14
Total deferred tax assets	54,779	48,620
Valuation allowance	(54,779)	(48,620)
Net deferred tax assets	$ 0	$ 0