Stock-Based Compensation - Assumptions (Details) - shares		12 Months Ended
	Dec. 31, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Employee and non-employee stock options
Stock Based Compensation
Options granted (in shares)		2,558,000
Employee stock options
Valuation of Stock Option Grants to Employees
Expected volatility, minimum		62.20%	69.70%	73.40%
Expected volatility, maximum		72.50%	78.80%	87.00%
Expected dividend rate		0.00%	0.00%	0.00%
Risk free interest rate, minimum		0.97%	1.56%	1.65%
Risk free interest rate, maximum		1.92%	2.32%	2.04%
Employee stock options | Minimum
Valuation of Stock Option Grants to Employees
Expected term		5 years 1 month 6 days	5 years 7 months 6 days	4 years 10 months 24 days
Employee stock options | Maximum
Valuation of Stock Option Grants to Employees
Expected term		5 years 2 months 12 days	10 years	7 years 1 month 6 days
Non-employee stock options
Stock Based Compensation
Options granted (in shares)	141,046
Options unvested (in shares)	10,456	10,456
Valuation of Stock Option Grants to Employees
Expected volatility, minimum		50.90%	70.20%	71.90%
Expected volatility, maximum		72.60%	75.40%	80.20%
Expected dividend rate		0.00%	0.00%	0.00%
Risk free interest rate, minimum		0.68%	1.74%	1.41%
Risk free interest rate, maximum		1.38%	2.24%	2.61%
Non-employee stock options | Minimum
Valuation of Stock Option Grants to Employees
Expected term		2 years 8 months 12 days	4 years 10 months 24 days	4 years 4 months 24 days
Non-employee stock options | Maximum
Valuation of Stock Option Grants to Employees
Expected term		3 years 2 months 12 days	9 years 9 months 18 days	10 years