Pension Plan - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Compensation And Retirement Disclosure [Abstract]
Amount of contributions to contributory plan	$ 67,100,000	$ 56,300,000	$ 56,600,000
Accumulated benefit obligation	123,200,000	117,500,000
Fair value of plan assets exceeded accumulated benefit obligation	8,400,000	$ 2,700,000
Estimated net loss that will be amortized from accumulated other comprehensive income over the next fiscal year	0
Estimated prior service cost that will be amortized from accumulated other comprehensive income over the next fiscal year	$ 0