Derivatives - Narrative (Detail) $ in Millions			12 Months Ended
	Aug. 31, 2016	Mar. 13, 2012 USD ($)	Dec. 31, 2017 USD ($) Agreement	Dec. 31, 2016 USD ($) Agreement	Dec. 31, 2015 USD ($)
Derivative [Line Items]
Repayment of debt			$ 201.6	$ 1,013.2	$ 272.7
Number of outstanding interest rate swap agreements | Agreement			0	0
Fair Value Hedging
Derivative [Line Items]
Reduction to interest expense				$ (1.0)	$ (2.0)
8.25% Senior Notes Due March 15, 2019
Derivative [Line Items]
Derivative, inception date				Mar. 13, 2012
Senior notes		$ 450.0
Interest rate	8.25%	8.25%
Maturity date	Mar. 15, 2019	Mar. 15, 2019		Mar. 15, 2019
Interest Rate Swap
Derivative [Line Items]
Terminated portion of interest rate swap agreement, notional amount				$ 190.0
Payment for termination of interest rate swaps				2.5
Not Designated as Hedging Instrument | Foreign Currency Contracts
Derivative [Line Items]
Aggregate notional value			$ 215.9	$ 172.2
Designated Fair Value Hedges | Interest Rate Swap
Derivative [Line Items]
Aggregate notional value		$ 400.0