Income Taxes - Income Tax Benefit Attributable to Our Loss from Operations (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Effective Income Tax Rate Reconciliation, Amount [Abstract]
U.S. federal income tax benefit at statutory rates	$ (6,286,000)	$ (5,591,000)
State income tax benefit, net of federal benefit	(565,000)	(502,000)
Research and experimentation credits	(303,000)	(268,000)
Change in tax rate	20,085,000
Deferred tax asset adjustment	37,000	65,000
Other	122,000	137,000
Change in valuation allowance	(13,151,000)	6,159,000
Income tax benefit	$ (61,000)	$ 0