Retirement Benefits - Fair Value 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 Plan Assets	$ 869,070	$ 732,502
Equity securities—U.S.
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	414,260	350,728
Equity securities—International
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	86,822	73,415
Debt securities
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	362,020	304,128
Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	$ 5,968	$ 4,231