Stock-Based Compensation - Assumptions (Details) - shares	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Employee and non-employee stock options
Stock Based Compensation
Options granted (in shares)			1,837,000
Employee stock options
Valuation of Stock Option Grants to Employees
Expected volatility, minimum	43.07%	40.59%	42.53%	40.28%
Expected volatility, maximum	45.84%	41.05%	45.84%	41.05%
Expected dividend rate	0.00%	0.00%	0.00%	0.00%
Risk free interest rate, minimum	1.60%	2.75%	1.60%	2.37%
Risk free interest rate, maximum	2.12%	2.97%	2.60%	2.97%
Employee stock options | Minimum
Valuation of Stock Option Grants to Employees
Expected term (years)	5 years 2 months 23 days	5 years 4 months 6 days	5 years 2 months 23 days	5 years 2 months 27 days
Employee stock options | Maximum
Valuation of Stock Option Grants to Employees
Expected term (years)	10 years	5 years 6 months	10 years	5 years 7 months 13 days
Non-employee stock options
Stock Based Compensation
Options granted (in shares)			91,073
Options unvested (in shares)	30,648		30,648
Valuation of Stock Option Grants to Employees
Expected term (years)		2 years 9 months 4 days
Expected volatility		41.36%
Expected volatility, minimum				41.36%
Expected volatility, maximum				42.03%
Expected dividend rate		0.00%		0.00%
Risk free interest rate		2.86%
Risk free interest rate, minimum				2.36%
Risk free interest rate, maximum				2.86%
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 9 months 4 days