Stock Based Compensation - Stock Options (Details) - $ / shares	3 Months Ended		12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
The activity related to stock option grants to employees and nonemployees
Outstanding at beginning (in shares)	2,498,606
Granted (in shares)	857,875	705,133
Forfeited (in shares)	(15,749)
Outstanding at end (in shares)	3,340,732		2,498,606
Vested and exercisable at end (in shares)	1,230,674
Vested and expected to vest at end (in shares)	3,340,732
Weighted average exercise price per share
Outstanding at beginning (in dollars per share)	$ 17.18
Granted (in dollars per share)	7.72
Forfeited (in dollars per share)	14.65
Outstanding at end (in dollars per share)	14.76		$ 17.18
Vested and exercisable at end (in dollars per share)	23.08
Vested and expected to vest at end (in dollars per share)	$ 14.76
Weighted-average remaining contractual life (years)
Outstanding (in years)	8 years		7 years 8 months 12 days
Vested and exercisable at end (in years)	5 years 9 months 18 days
Vested and expected to vest at end (in years)	8 years