Stock-Based Compensation - Assumptions (Details) - shares	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Employee and non-employee stock options
Stock Based Compensation
Options granted (in shares)			1,921,000
Employee stock options
Valuation of Stock Option Grants to Employees
Expected volatility, minimum	62.30%	69.00%	62.30%	68.50%
Expected volatility, maximum	62.50%	72.50%	62.90%	72.50%
Expected dividend rate	0.00%	0.00%	0.00%	0.00%
Risk free interest rate, minimum	1.67%	0.97%	1.67%	0.97%
Risk free interest rate, maximum	1.90%	1.12%	1.90%	1.24%
Employee stock options | Minimum
Valuation of Stock Option Grants to Employees
Expected term (years)			5 years 1 month 6 days	5 years 1 month 6 days
Employee stock options | Maximum
Valuation of Stock Option Grants to Employees
Expected term (years)	5 years 2 months 12 days	5 years 2 months 12 days	5 years 2 months 12 days	5 years 2 months 12 days
Non-employee stock options
Stock Based Compensation
Options granted (in shares)			136,046
Options unvested (in shares)	5,166		5,166
Valuation of Stock Option Grants to Employees
Expected term (years)	2 years 8 months 12 days	2 years 9 months 18 days	2 years 8 months 12 days
Expected volatility	51.30%	50.90%
Expected volatility, minimum			51.30%	50.90%
Expected volatility, maximum			52.20%	72.60%
Expected dividend rate	0.00%	0.00%	0.00%	0.00%
Risk free interest rate	1.58%	0.85%
Risk free interest rate, minimum			1.42%	0.68%
Risk free interest rate, maximum			1.58%	0.90%
Non-employee stock options | Minimum
Valuation of Stock Option Grants to Employees
Expected term (years)				2 years 9 months 18 days
Non-employee stock options | Maximum
Valuation of Stock Option Grants to Employees
Expected term (years)				3 years 2 months 12 days