Equity-Based Compensation - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended	3 Months Ended		6 Months Ended
	Jan. 31, 2020	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized equity-based compensation expense related to restricted stock		$ 2.3		$ 2.3
Potential dilutive securities excluded from computation of diluted net loss per common share		7,829,000	5,388,000	7,829,000	5,388,000
Number of Shares, Granted				181,020
Weighted Average Grant Date Fair Value per Share, Granted				$ 15.05
Weighted average grant date fair value per share		$ 9.04	$ 9.22	$ 8.16	$ 9.07
Total intrinsic value of stock options exercised		$ 0.5	$ 1.3	$ 0.8	$ 1.5
Unrecognized compensation cost related to stock options		$ 39.1		$ 39.1
Stock options outstanding		7,581,040		7,581,040		5,365,971
Vesting description				that vest upon obtaining certain scientific, financial and regulatory milestones through 2020
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average period of unrecognized compensation costs				2 years 3 months 18 days
Performance Based RSUs [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Potential dilutive securities excluded from computation of diluted net loss per common share				71,875
RSUs [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Remaining vesting period	3 years
Number of Shares, Granted	181,020
Weighted Average Grant Date Fair Value per Share, Granted	$ 15.05
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average period of unrecognized compensation costs				2 years 8 months 12 days
Performance Based Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Potential dilutive securities excluded from computation of diluted net loss per common share				143,750
Stock options outstanding		183,750		183,750
2015 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Remaining vesting period				3 years
Description of stock options granted under the Plan				Stock options granted under the 2015 Plan generally vest 25% on the first anniversary of the original vesting date, with the balance vesting monthly over the remaining three years, unless they contain specific performance-based vesting provisions. The maximum term of stock options granted under the 2015 Plan is ten years.
Shares available for future issuance		2,104,706		2,104,706
Percentage of cumulative increase in number of shares for future issuance				4.00%
2015 Plan [Member] | First Anniversary of Original Vesting Date [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vest percentage on the first anniversary				25.00%
Maximum [Member] | 2015 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum term of stock options granted				10 years