Retirement Plans - Summary of Plan's Assets Carried at Fair Value (Detail) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plan Disclosure [Line Items]
Total fair value	$ 207.8	$ 207.5	$ 217.2
Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total fair value	108.1	106.8
Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total fair value	$ 99.7	$ 100.7	$ 101.1