Income Taxes - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Decrease in deferred tax assets	$ 12,658,000
Net impact to income tax expense due to tax act	0
Operating Loss Carryforwards [Line Items]
Valuation allowance increase (decrease)	(8,489,000)	$ 6,800,000	$ 11,296,000
NOL carryforward, decrease	1,506,000
Net income (loss)	$ (15,002,000)	$ (22,526,000)	$ (30,236,000)
Permanent differences	(14.74%)	(7.87%)	(4.90%)
Unrecognized tax benefits that would impact effective tax rate	$ 1,057,000	$ 800,000
Research Tax Credit Carryforward
Operating Loss Carryforwards [Line Items]
Tax credit carryforward	3,200,000	$ 4,230,000
Research and development credits, decrease	$ 32,000