Retirement Plans - Reconciliation of Balances of Pension Benefit Obligation and Fair Value of Plan Assets (Detail) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Pension Plans and Defined Benefit Postretirement Plans Disclosure [Abstract]
Benefit obligation at beginning of year		$ 261.8	$ 272.0
Service cost		1.5	1.1	$ 0.7
Interest cost		10.8	10.8	12.7
Net actuarial loss (gain)		1.8	(10.4)
Benefits paid	$ (43.3)	(14.6)	(11.7)
Benefit obligation at end of year	272.0	261.3	261.8	272.0
Fair value of plan assets at beginning of year		207.5	217.2
Actual return on plan assets		14.9	2.0
Contributions by the company		0.0	0.0	0.0
Benefits paid	(43.3)	(14.6)	(11.7)
Fair value of plan assets at end of year	$ 217.2	207.8	207.5	$ 217.2
Funded status of the plan (underfunded)		(53.5)	(54.3)
Noncurrent liabilities - accrued benefit liability		(53.5)	(54.3)
Accumulated other comprehensive loss - net actuarial loss		67.9	71.8
Net amount included in retained earnings		$ 14.4	$ 17.5