401(k) savings plan - Additional Information (Detail) - 401 (k) - USD ($) $ in Millions	1 Months Ended		12 Months Ended
	Mar. 31, 2020	Feb. 28, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Contribution Plan Disclosure [Line Items]
Contributions to the 401(k) Plan		$ 2.4
Expenses related to 401(k) Plan			$ 4.6	$ 2.4	$ 1.5
Scenario, Forecast
Defined Contribution Plan Disclosure [Line Items]
Contributions to the 401(k) Plan	$ 4.6