Pension and Employee Benefit Plans - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Compensation And Retirement Disclosure [Abstract]
Defined benefit plan contributions	$ 1.8	$ 0.1	$ 0.4
Unfunded liability plans		$ 8.6		$ 8.9