Equity-Based Compensation - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized equity-based compensation expense related to restricted stock	$ 0.2
Potential dilutive securities excluded from computation of diluted net loss per common share	5,438,000	5,147,000	5,185,000
Weighted average grant date fair value per share	$ 9.21	$ 15.05	$ 12.43
Total intrinsic value of stock options exercised	$ 2.3	$ 18.0	$ 1.6
Unrecognized compensation cost related to stock options	$ 28.2
Stock options outstanding	5,365,971	5,037,663
Vesting description	performance-based stock options 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 grant date fair value of restricted stock, granted		$ 22.98
Restricted stock granted	0		0
Weighted average period of unrecognized compensation costs	1 year
Performance Based Restricted Stock Units [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
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average period of unrecognized compensation costs	2 years 6 months
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	188,750
Stock options outstanding	213,750
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	2,655,673
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