Share-Based Payments - Inducement Awards Outside of the 2019 Inducement Plan (Details) - USD ($)	1 Months Ended	12 Months Ended
	Jul. 31, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-Based Payments
Share-based compensation expense		$ 5,219,000	$ 9,748,000	$ 5,154,000
Additional disclosures
Weighted-average remaining contractual life		8 years 8 months 12 days
Inducement Awards Outside of the 2019 Inducement Plan
Share-Based Payments
Share-based compensation expense		$ 400,000	$ 400,000
Fair Value Assumptions
Expected volatility (as a percent)		59.80%
Expected term of options (in years)		6 years 1 month 6 days
Risk-free interest rate (as a percent)		2.90%
Dividend yield (as a percent)		0.00%
Additional disclosures
Weighted-average remaining contractual life		7 years 7 months 6 days
Total unrecognized compensation related to unvested options		$ 700,000
Recognition period		9 months 18 days
Inducement Awards Outside of the 2019 Inducement Plan | Vesting period, year one
Share-Based Payments
Percentage that vests during the period	25.00%
Inducement Awards Outside of the 2019 Inducement Plan | Vesting period, years 2-4
Share-Based Payments
Percentage that vests during the period	75.00%
Monthly vesting period	36 months
Inducement Awards Outside of the 2019 Inducement Plan | Non-statutory option
Share-Based Payments
Vesting period	4 years
Options exercise price (in dollars per share)	$ 35.30
Exercise period	10 years
Options weighted average grant date fair value (in dollars per share)		$ 20.50
Inducement Awards Outside of the 2019 Inducement Plan | Non-statutory option | Chief Executive Officer
Share-Based Payments
Options granted during the period	85,000
Inducement Awards Outside of the 2019 Inducement Plan | Restricted Stock Units ("RSUs")
Share-Based Payments
Granted		$ 35.30
Inducement Awards Outside of the 2019 Inducement Plan | Restricted Stock Units ("RSUs") | Chief Executive Officer
Share-Based Payments
Restricted stock granted during the period	15
Inducement Awards Outside of the 2019 Inducement Plan | Restricted Stock Units ("RSUs") | Upon receipt of FDA approval
Share-Based Payments
Percentage that vests during the period	50.00%
Inducement Awards Outside of the 2019 Inducement Plan | Restricted Stock Units ("RSUs") | First anniversary of FDA approval
Share-Based Payments
Percentage that vests during the period	50.00%
2019 Inducement Plan
Share-Based Payments
Options granted during the period		18,200	70,315
Options exercise price (in dollars per share)		$ 19.04	$ 21.45
Options weighted average grant date fair value (in dollars per share)		$ 7.93
Share-based compensation expense		$ 38,000,000	$ 77,000