Pension Plan - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Compensation And Retirement Disclosure [Abstract]
Amount of contributions to contributory plan	$ 56,600,000	$ 50,100,000	$ 45,700,000
Accumulated benefit obligation	108,300,000	115,900,000
Fair value of plan assets exceeded accumulated benefit obligation		$ 2,700,000
Fair value of plan accumulated benefit obligation exceeds plan assets	3,700,000
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