Employee Benefits - Postretirement Benefits Other Than Pension Expenses (Detail) - Defined Contribution and Other Retirement Plans - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Defined Benefit Plan Disclosure [Line Items]
Service cost for benefits earned	$ 143	$ 148	$ 286	$ 296
Interest cost on projected benefit obligation	475	578	949	1,156
Net amortization and deferrals	(1,152)	(1,195)	(2,305)	(2,389)
Net periodic benefit (income) cost	$ (534)	$ (469)	$ (1,070)	$ (937)