Retirement Plans - Periodic Pension Cost, Next Fiscal Year (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Interest cost		$ 1,144	$ 1,086	$ 1,189
Estimated 2020 net periodic pension cost		$ 1,353	$ 1,524	$ 1,558
Scenario, Forecast [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost	$ 1,004
Amortization of actuarial loss	289
Estimated 2020 net periodic pension cost	$ 1,293