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Stock-based Compensation - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total unrecognized compensation expense related to stock options	$ 93,300		$ 93,300
Stock-based compensation expense	14,773	$ 9,067	37,667	$ 25,216
Departing Employee [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense			2,200
Non-Employees [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense			$ 2,900
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense, remaining weighted-average period for recognition			2 years 9 months 18 days
Restricted Common Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense, remaining weighted-average period for recognition			1 year 5 months 1 day
Total unrecognized compensation expense	$ 10,500		$ 10,500