Stock-Based Compensation - Assumptions (Details) - shares	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Employee and non-employee stock options
Stock Based Compensation
Options granted (in shares)			1,568,000
Employee stock options
Valuation of Stock Option Grants to Employees
Expected volatility, minimum	62.70%	68.50%	62.70%	68.50%
Expected volatility, maximum	62.90%	69.20%	62.90%	71.00%
Expected dividend rate	0.00%	0.00%	0.00%	0.00%
Risk free interest rate, minimum	1.80%	1.18%	1.80%	1.18%
Risk free interest rate, maximum	1.87%	1.24%	1.91%	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	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)	6,930		6,930
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	52.20%	56.50%
Expected volatility, minimum			51.70%	56.50%
Expected volatility, maximum			52.20%	72.60%
Expected dividend rate	0.00%	0.00%	0.00%	0.00%
Risk free interest rate	1.50%	0.68%
Risk free interest rate, minimum			1.42%	0.68%
Risk free interest rate, maximum			1.50%	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