Pensions and Other Post-retirement Benefits - Summary of Pension Plan Assets Measured at Fair Value on Recurring Basis by Fair Value Hierarchy (Detail) - Pension Plan - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets measured at fair value	$ 586,822	$ 515,858	$ 443,112
Fair Value, Measurements, Recurring
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets measured at fair value	586,822	515,858
Plan assets at NAV	196,647	159,614
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets measured at fair value	294,108	253,976
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets measured at fair value	71,671	80,766
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets measured at fair value	24,396	21,502
Fair Value, Measurements, Recurring | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets measured at fair value	283,516	235,491
Plan assets at NAV	66,847	56,449
Fair Value, Measurements, Recurring | Equity securities | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets measured at fair value	216,669	179,042
Fair Value, Measurements, Recurring | Equity securities | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets measured at fair value	0	0
Fair Value, Measurements, Recurring | Equity securities | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets measured at fair value	0	0
Fair Value, Measurements, Recurring | Fixed income securities
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets measured at fair value	148,173	154,640
Plan assets at NAV	0	0
Fair Value, Measurements, Recurring | Fixed income securities | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets measured at fair value	76,502	73,874
Fair Value, Measurements, Recurring | Fixed income securities | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets measured at fair value	71,671	80,766
Fair Value, Measurements, Recurring | Fixed income securities | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets measured at fair value	0	0
Fair Value, Measurements, Recurring | Pooled investment funds
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets measured at fair value	123,119	97,373
Plan assets at NAV	123,119	97,373
Fair Value, Measurements, Recurring | Pooled investment funds | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets measured at fair value	0	0
Fair Value, Measurements, Recurring | Pooled investment funds | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets measured at fair value	0	0
Fair Value, Measurements, Recurring | Pooled investment funds | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets measured at fair value	0	0
Fair Value, Measurements, Recurring | Insurance contracts
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets measured at fair value	24,396	21,502
Plan assets at NAV	0	0
Fair Value, Measurements, Recurring | Insurance contracts | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets measured at fair value	0	0
Fair Value, Measurements, Recurring | Insurance contracts | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets measured at fair value	0	0
Fair Value, Measurements, Recurring | Insurance contracts | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets measured at fair value	24,396	21,502
Fair Value, Measurements, Recurring | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets measured at fair value	7,618	6,852
Plan assets at NAV	6,681	5,792
Fair Value, Measurements, Recurring | Cash and cash equivalents | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets measured at fair value	937	1,060
Fair Value, Measurements, Recurring | Cash and cash equivalents | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets measured at fair value	0	0
Fair Value, Measurements, Recurring | Cash and cash equivalents | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets measured at fair value	$ 0	$ 0