Stockholders' Equity - Stock Option Activity (Details)	9 Months Ended
	Sep. 30, 2019 USD ($) $ / shares shares	Sep. 30, 2018 shares
Number of shares
Beginning balance outstanding (in shares) | shares	2,282,636
Granted (in shares) | shares	1,197,231
Exercised (in shares) | shares	(241,757)	0
Forfeited (in shares) | shares	(53,268)
Ending balance outstanding (in shares) | shares	3,184,842
Vested and expected to vest (in shares) | shares	3,168,673
Exercisable (in shares) | shares	1,612,322
Weighted average exercise price
Beginning balance outstanding (in dollars per share) | $ / shares	$ 5.06
Granted (in dollars per share) | $ / shares	15.57
Exercised (in dollars per share) | $ / shares	4.55
Forfeited (in dollars per share) | $ / shares	7.50
Ending balance outstanding (in dollars per share) | $ / shares	9.01
Vested and expected to vest (in dollars per share) | $ / shares	9.05
Exercisable (in dollars per share) | $ / shares	$ 6.34
Weighted average contractual term
Outstanding (in years)	8 years
Vested and expected to vest (in years)	8 years
Exercisable (in years)	6 years 7 months 6 days
Aggregate intrinsic value
Outstanding (in dollars) | $	$ 36,930,345
Vested and expected to vest (in dollars) | $	36,632,902
Exercisable (in dollars) | $	22,428,613
Intinsic value of exercised options | $	$ 4,300,000