Pension Plan - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Defined Benefit Plan Disclosure [Line Items]
Amount of contributions to contributory plan		$ 40.7	$ 35.7	$ 29.9
Accumulated benefit obligation		117.7	126.4
Fair value of plan assets exceeded accumulated benefit obligation		$ 10.9	$ 9.7
Scenario, Forecast
Defined Benefit Plan Disclosure [Line Items]
Estimated net loss that will be amortized from accumulated other comprehensive income over the next fiscal year	$ (3.1)