Stock-Based Compensation - Assumptions (Details) - shares	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Employee and non-employee stock options
Stock Based Compensation
Options granted (in shares)	1,150,000
Employee stock options
Valuation of Stock Option Grants to Employees
Expected term (years)		5 years 1 month 6 days
Expected volatility		62.71%
Expected volatility, minimum	40.28%
Expected dividend rate	0.00%	0.00%
Risk free interest rate, maximum		1.91%
Employee stock options | Minimum
Valuation of Stock Option Grants to Employees
Expected term (years)	5 years 2 months 27 days
Risk free interest rate, minimum	2.37%
Employee stock options | Maximum
Valuation of Stock Option Grants to Employees
Expected term (years)	5 years 7 months 2 days
Expected volatility, maximum	40.88%
Risk free interest rate, maximum	2.70%
Non-employee stock options
Stock Based Compensation
Options granted (in shares)	105,448
Options unvested (in shares)	7,301
Valuation of Stock Option Grants to Employees
Expected term (years)		2 years 8 months 1 day
Expected volatility		51.69%
Expected volatility, minimum	41.48%
Expected volatility, maximum	41.71%
Expected dividend rate	0.00%	0.00%
Risk free interest rate		1.42%
Risk free interest rate, minimum	2.36%
Risk free interest rate, maximum	2.40%
Non-employee stock options | Minimum
Valuation of Stock Option Grants to Employees
Expected term (years)	2 years 8 months 19 days
Non-employee stock options | Maximum
Valuation of Stock Option Grants to Employees
Expected term (years)	2 years 8 months 27 days