Pension and Postretirement Benefits - Fair Values of Plan Assets by Asset Category (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	$ 470,101	$ 402,579
Corporate Debt Securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	149,409	140,836
Residential Mortgage-Backed Securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	4,041	4,644
Mutual Fund
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	25,594	9,161
Consumer Goods
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	46,260	44,746
Energy and Utilities
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	27,410	23,844
Finance
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	57,900	45,131
Equity Securities Healthcare
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	37,017	31,259
Industrials
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	17,996	16,033
Information Technology
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	60,225	47,226
Other
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	35,597	28,963
Commercial Paper
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	2,948	6,836
Other
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	5,106	2,769
Unallocated Group Annuity Contract
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	598	1,131
Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	313,105	249,077
Level 1 | Mutual Fund
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	25,594	9,161
Level 1 | Consumer Goods
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	46,260	44,746
Level 1 | Energy and Utilities
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	27,410	23,844
Level 1 | Finance
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	57,900	45,131
Level 1 | Equity Securities Healthcare
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	37,017	31,259
Level 1 | Industrials
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	17,996	16,033
Level 1 | Information Technology
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	60,225	47,226
Level 1 | Other
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	35,597	28,963
Level 1 | Other
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	5,106	2,714
Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	156,996	153,502
Level 2 | Corporate Debt Securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	149,409	140,836
Level 2 | Residential Mortgage-Backed Securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	4,041	4,644
Level 2 | Commercial Paper
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	2,948	6,836
Level 2 | Other
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0	55
Level 2 | Unallocated Group Annuity Contract
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	$ 598	$ 1,131