Retirement Plans and Other Post-Retirement Benefits - Schedule of Fair Value of Benefit Plan Assets (Detail) $ in Millions	Dec. 31, 2018 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 333.2
Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	41.8
Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	291.4
Fixed Income [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	330.9
Fixed Income [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	41.8
Fixed Income [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	289.1
Cash and Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2.3
Cash and Equivalents [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 2.3