Pensions and Postretirement Benefits Other than Pensions - Assets of U.S and U.K Plans Using Fair Value Hierarchy (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
United States
Defined Benefit Plan Disclosure [Line Items]
Fair market value of plan assets	$ 1,047,214	$ 912,129
United Kingdom plan
Defined Benefit Plan Disclosure [Line Items]
Fair market value of plan assets	377,536	347,108
Quoted Prices in Active Markets for Identical Assets Level (1) | United States
Defined Benefit Plan Disclosure [Line Items]
Fair market value of plan assets	23,867	23,896
Quoted Prices in Active Markets for Identical Assets Level (1) | United Kingdom plan
Defined Benefit Plan Disclosure [Line Items]
Fair market value of plan assets	333,497	304,754
Significant Other Observable Inputs Level (2) | United States
Defined Benefit Plan Disclosure [Line Items]
Fair market value of plan assets	22,410	10,514
Significant Other Observable Inputs Level (2) | United Kingdom plan
Defined Benefit Plan Disclosure [Line Items]
Fair market value of plan assets	13,859	13,416
Significant Unobservable Inputs Level (3) | United States
Defined Benefit Plan Disclosure [Line Items]
Fair market value of plan assets	0	0
Significant Unobservable Inputs Level (3) | United Kingdom plan
Defined Benefit Plan Disclosure [Line Items]
Fair market value of plan assets	30,180	28,938	$ 38,070	$ 33,796
Fair Value Measured at Net Asset Value Per Share | United States
Defined Benefit Plan Disclosure [Line Items]
Fair market value of plan assets	1,000,937	877,719
Fair Value Measured at Net Asset Value Per Share | United Kingdom plan
Defined Benefit Plan Disclosure [Line Items]
Fair market value of plan assets	0	0
Cash and cash equivalents | United States
Defined Benefit Plan Disclosure [Line Items]
Fair market value of plan assets	23,867	23,896
Cash and cash equivalents | United Kingdom plan
Defined Benefit Plan Disclosure [Line Items]
Fair market value of plan assets	1,802	1,644
Cash and cash equivalents | Quoted Prices in Active Markets for Identical Assets Level (1) | United States
Defined Benefit Plan Disclosure [Line Items]
Fair market value of plan assets	23,867	23,896
Cash and cash equivalents | Quoted Prices in Active Markets for Identical Assets Level (1) | United Kingdom plan
Defined Benefit Plan Disclosure [Line Items]
Fair market value of plan assets	1,802	1,644
Cash and cash equivalents | Significant Other Observable Inputs Level (2) | United States
Defined Benefit Plan Disclosure [Line Items]
Fair market value of plan assets	0	0
Cash and cash equivalents | Significant Other Observable Inputs Level (2) | United Kingdom plan
Defined Benefit Plan Disclosure [Line Items]
Fair market value of plan assets	0	0
Cash and cash equivalents | Significant Unobservable Inputs Level (3) | United States
Defined Benefit Plan Disclosure [Line Items]
Fair market value of plan assets	0	0
Cash and cash equivalents | Significant Unobservable Inputs Level (3) | United Kingdom plan
Defined Benefit Plan Disclosure [Line Items]
Fair market value of plan assets	0	0
Cash and cash equivalents | Fair Value Measured at Net Asset Value Per Share | United States
Defined Benefit Plan Disclosure [Line Items]
Fair market value of plan assets	0	0
Cash and cash equivalents | Fair Value Measured at Net Asset Value Per Share | United Kingdom plan
Defined Benefit Plan Disclosure [Line Items]
Fair market value of plan assets	0	0
Collective Trust Funds - Equity | United States
Defined Benefit Plan Disclosure [Line Items]
Fair market value of plan assets	309,794	238,795
Collective Trust Funds - Equity | Quoted Prices in Active Markets for Identical Assets Level (1) | United States
Defined Benefit Plan Disclosure [Line Items]
Fair market value of plan assets	0	0
Collective Trust Funds - Equity | Significant Other Observable Inputs Level (2) | United States
Defined Benefit Plan Disclosure [Line Items]
Fair market value of plan assets	0	0
Collective Trust Funds - Equity | Significant Unobservable Inputs Level (3) | United States
Defined Benefit Plan Disclosure [Line Items]
Fair market value of plan assets	0	0
Collective Trust Funds - Equity | Fair Value Measured at Net Asset Value Per Share | United States
Defined Benefit Plan Disclosure [Line Items]
Fair market value of plan assets	309,794	238,795
Collective Trust Funds - Fixed income | United States
Defined Benefit Plan Disclosure [Line Items]
Fair market value of plan assets	682,279	622,576
Collective Trust Funds - Fixed income | Quoted Prices in Active Markets for Identical Assets Level (1) | United States
Defined Benefit Plan Disclosure [Line Items]
Fair market value of plan assets	0	0
Collective Trust Funds - Fixed income | Significant Other Observable Inputs Level (2) | United States
Defined Benefit Plan Disclosure [Line Items]
Fair market value of plan assets	22,410	10,514
Collective Trust Funds - Fixed income | Significant Unobservable Inputs Level (3) | United States
Defined Benefit Plan Disclosure [Line Items]
Fair market value of plan assets	0	0
Collective Trust Funds - Fixed income | Fair Value Measured at Net Asset Value Per Share | United States
Defined Benefit Plan Disclosure [Line Items]
Fair market value of plan assets	659,869	612,062
Collective Trust Funds - Real Estate | United States
Defined Benefit Plan Disclosure [Line Items]
Fair market value of plan assets	31,274	26,862
Collective Trust Funds - Real Estate | Quoted Prices in Active Markets for Identical Assets Level (1) | United States
Defined Benefit Plan Disclosure [Line Items]
Fair market value of plan assets	0	0
Collective Trust Funds - Real Estate | Significant Other Observable Inputs Level (2) | United States
Defined Benefit Plan Disclosure [Line Items]
Fair market value of plan assets	0	0
Collective Trust Funds - Real Estate | Significant Unobservable Inputs Level (3) | United States
Defined Benefit Plan Disclosure [Line Items]
Fair market value of plan assets	0	0
Collective Trust Funds - Real Estate | Fair Value Measured at Net Asset Value Per Share | United States
Defined Benefit Plan Disclosure [Line Items]
Fair market value of plan assets	31,274	26,862
Equity securities | United Kingdom plan
Defined Benefit Plan Disclosure [Line Items]
Fair market value of plan assets	72,503	58,848
Equity securities | Quoted Prices in Active Markets for Identical Assets Level (1) | United Kingdom plan
Defined Benefit Plan Disclosure [Line Items]
Fair market value of plan assets	72,503	58,848
Equity securities | Significant Other Observable Inputs Level (2) | United Kingdom plan
Defined Benefit Plan Disclosure [Line Items]
Fair market value of plan assets	0	0
Equity securities | Significant Unobservable Inputs Level (3) | United Kingdom plan
Defined Benefit Plan Disclosure [Line Items]
Fair market value of plan assets	0	0
Equity securities | Fair Value Measured at Net Asset Value Per Share | United Kingdom plan
Defined Benefit Plan Disclosure [Line Items]
Fair market value of plan assets	0	0
Fixed income securities | United Kingdom plan
Defined Benefit Plan Disclosure [Line Items]
Fair market value of plan assets	259,192	244,262
Fixed income securities | Quoted Prices in Active Markets for Identical Assets Level (1) | United Kingdom plan
Defined Benefit Plan Disclosure [Line Items]
Fair market value of plan assets	259,192	244,262
Fixed income securities | Significant Other Observable Inputs Level (2) | United Kingdom plan
Defined Benefit Plan Disclosure [Line Items]
Fair market value of plan assets	0	0
Fixed income securities | Significant Unobservable Inputs Level (3) | United Kingdom plan
Defined Benefit Plan Disclosure [Line Items]
Fair market value of plan assets	0	0
Fixed income securities | Fair Value Measured at Net Asset Value Per Share | United Kingdom plan
Defined Benefit Plan Disclosure [Line Items]
Fair market value of plan assets	0	0
Other investments | United Kingdom plan
Defined Benefit Plan Disclosure [Line Items]
Fair market value of plan assets	44,039	42,354
Other investments | Quoted Prices in Active Markets for Identical Assets Level (1) | United Kingdom plan
Defined Benefit Plan Disclosure [Line Items]
Fair market value of plan assets	0	0
Other investments | Significant Other Observable Inputs Level (2) | United Kingdom plan
Defined Benefit Plan Disclosure [Line Items]
Fair market value of plan assets	13,859	13,416
Other investments | Significant Unobservable Inputs Level (3) | United Kingdom plan
Defined Benefit Plan Disclosure [Line Items]
Fair market value of plan assets	30,180	28,938
Other investments | Fair Value Measured at Net Asset Value Per Share | United Kingdom plan
Defined Benefit Plan Disclosure [Line Items]
Fair market value of plan assets	$ 0	$ 0