Retirement Plans and Other Postretirement Benefits - Reconciliation of Beginning and Ending Balances for Measurements in Hierarchy Level 3 (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Beginning balance	$ 4,155	$ 4,210
Total unrealized (losses) or gains	110	0
Total realized gains or (losses)	0	0
Purchases	600	845
Maturities/redemptions	(1,365)	(900)
Ending balance	3,500	4,155
Certificates of Deposit [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Beginning balance	4,155	4,210
Total unrealized (losses) or gains	110	0
Total realized gains or (losses)	0	0
Purchases	600	845
Maturities/redemptions	(1,365)	(900)
Ending balance	$ 3,500	$ 4,155