Employee Benefits - Postretirement Benefits Other Than Pension Expenses (Detail) - Defined Contribution and Other Retirement Plans - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Defined Benefit Plan Disclosure [Line Items]
Service cost for benefits earned	$ 142	$ 148	$ 428	$ 444
Interest cost on projected benefit obligation	474	578	1,423	1,734
Net amortization and deferrals	(1,153)	(1,195)	(3,458)	(3,584)
Net periodic benefit (income) cost	$ (537)	$ (469)	$ (1,607)	$ (1,406)