Organization and Summary of Significant Accounting Policies - Assumptions Used in Determining the Fair Value of Warrant Liabilities (Details) - Significant Unobservable Inputs (Level 3) - Warrants - $ / shares	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Dividend yield (as a percent)	0.00%	0.00%
Weighted average fair value (in usd per share)	$ 0.73	$ 0.49
Minimum
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Risk-free interest rate (as a percent)	1.93%	1.64%
Volatility	87.72%	77.25%
Expected term	5 years 3 months 15 days	4 years 9 months
Maximum
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Risk-free interest rate (as a percent)	1.94%	1.99%
Volatility	88.33%	81.03%
Expected term	5 years 5 months 1 day	6 years 2 months 1 day