Fair Value and Carrying Value of Long-Term Debt (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Debt Instrument [Line Items]
Fair value of interest rate swap	$ 24.8	$ 20.5
Twenty Ten Senior Notes [Member]
Debt Instrument [Line Items]
Fair value of interest rate swap	2.1	0
Debt Instrument Unamortized Discount	2.0	2.2
Series Two Thousand Five Dash One Notes [Member]
Debt Instrument [Line Items]
Fair value of interest rate swap		10.3
Two Thousand Fourteen Senior Notes Five Year [Member]
Debt Instrument [Line Items]
Fair value of interest rate swap	1.3	0
Debt Instrument Unamortized Discount	0.7	0
Two Thousand Fourteen Senior Notes Thirty Year [Member]
Debt Instrument [Line Items]
Fair value of interest rate swap		0
Debt Instrument Unamortized Discount	$ 1.6

Fair value before effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 20

-Section 55

-Paragraph 7

-URI http://asc.fasb.org/extlink&oid=28370219&loc=SL20226000-175313

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 20

-Section 50

-Paragraph 3

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=20225523&loc=SL20225862-175312

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 4B

-Subparagraph (a),(c)

-URI http://asc.fasb.org/extlink&oid=7476318&loc=SL5624163-113959

Name:	us-gaap_DerivativeFairValueOfDerivativeAsset
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant