Changes in Accumulated Other Comprehensive Income (Loss) (Additional Information) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Actuarial gains (losses), net of tax	$ (3.0)	$ (0.6)	$ (6.1)
Actuarial (losses) gains, tax expense (benefit)	(1.6)	(0.4)	(3.7)
Amortization of actuarial losses, net of tax	0.6	0.5	3.5
Amortization of actuarial losses, tax expense (benefit)	$ (0.4)	$ (0.3)	(2.1)
Pension settlement costs, net of tax			3.0
Pension settlement costs, tax expense (benefit)			$ (1.9)