Summary of Pension Plan Assets by Category Based on Hierarchy of Fair Value Measurements (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Schedule Of Pension And Other Retirement Benefits Changes In Benefit Obligation And Fair Value Of Plan Assets [Line Items]
Percent of total assets	100.00%	100.00%
Cash and Cash Equivalents
Schedule Of Pension And Other Retirement Benefits Changes In Benefit Obligation And Fair Value Of Plan Assets [Line Items]
Balance	$ 0.4	$ 0.2
Percent of total assets	0.00%	0.00%
Emerging Markets Equity Fund
Schedule Of Pension And Other Retirement Benefits Changes In Benefit Obligation And Fair Value Of Plan Assets [Line Items]
Balance	14.6	13.3
Percent of total assets	7.00%	8.00%
Common/Collective Trust Funds - Convertible Securities
Schedule Of Pension And Other Retirement Benefits Changes In Benefit Obligation And Fair Value Of Plan Assets [Line Items]
Balance	6.3	4.8
Percent of total assets	3.00%	3.00%
Private Real Estate Fund
Schedule Of Pension And Other Retirement Benefits Changes In Benefit Obligation And Fair Value Of Plan Assets [Line Items]
Balance	15.6	12.1
Percent of total assets	8.00%	7.00%
Equity Securities
Schedule Of Pension And Other Retirement Benefits Changes In Benefit Obligation And Fair Value Of Plan Assets [Line Items]
Balance	132.6	100.1
Percent of total assets	65.00%	60.00%
Equity Securities | U.S. Large-Cap
Schedule Of Pension And Other Retirement Benefits Changes In Benefit Obligation And Fair Value Of Plan Assets [Line Items]
Balance	44.5	32.0
Percent of total assets	22.00%	19.00%
Equity Securities | U.S. Small And Mid-Cap
Schedule Of Pension And Other Retirement Benefits Changes In Benefit Obligation And Fair Value Of Plan Assets [Line Items]
Balance	15.3	10.7
Percent of total assets	7.00%	6.00%
Equity Securities | International
Schedule Of Pension And Other Retirement Benefits Changes In Benefit Obligation And Fair Value Of Plan Assets [Line Items]
Balance	58.2	44.1
Percent of total assets	29.00%	27.00%
Fixed Income Securities
Schedule Of Pension And Other Retirement Benefits Changes In Benefit Obligation And Fair Value Of Plan Assets [Line Items]
Balance	49.7	50.4
Percent of total assets	24.00%	30.00%
Fixed Income Securities | Long-term government/treasury bonds
Schedule Of Pension And Other Retirement Benefits Changes In Benefit Obligation And Fair Value Of Plan Assets [Line Items]
Balance	13.7	13.8
Percent of total assets	7.00%	8.00%
Fixed Income Securities | Long-term investment grade corporate bonds
Schedule Of Pension And Other Retirement Benefits Changes In Benefit Obligation And Fair Value Of Plan Assets [Line Items]
Balance	15.4	17.5
Percent of total assets	7.00%	11.00%
Fixed Income Securities | U.S. Treasury Inflation-Protected Securities (TIPs)
Schedule Of Pension And Other Retirement Benefits Changes In Benefit Obligation And Fair Value Of Plan Assets [Line Items]
Balance	8.7	8.5
Percent of total assets	4.00%	5.00%
Fixed Income Securities | Emerging Markets Bonds
Schedule Of Pension And Other Retirement Benefits Changes In Benefit Obligation And Fair Value Of Plan Assets [Line Items]
Balance	5.8	5.4
Percent of total assets	3.00%	3.00%
Fixed Income Securities | High Yield Bonds
Schedule Of Pension And Other Retirement Benefits Changes In Benefit Obligation And Fair Value Of Plan Assets [Line Items]
Balance	6.1	5.2
Percent of total assets	3.00%	3.00%
Total Other Investment
Schedule Of Pension And Other Retirement Benefits Changes In Benefit Obligation And Fair Value Of Plan Assets [Line Items]
Balance	21.9	16.9
Percent of total assets	11.00%	10.00%
Level 1
Schedule Of Pension And Other Retirement Benefits Changes In Benefit Obligation And Fair Value Of Plan Assets [Line Items]
Balance	14.6	13.3
Level 1 | Cash and Cash Equivalents
Schedule Of Pension And Other Retirement Benefits Changes In Benefit Obligation And Fair Value Of Plan Assets [Line Items]
Balance	0
Level 1 | Emerging Markets Equity Fund
Schedule Of Pension And Other Retirement Benefits Changes In Benefit Obligation And Fair Value Of Plan Assets [Line Items]
Balance	14.6	13.3
Level 1 | Common/Collective Trust Funds - Convertible Securities
Schedule Of Pension And Other Retirement Benefits Changes In Benefit Obligation And Fair Value Of Plan Assets [Line Items]
Balance	0
Level 1 | Private Real Estate Fund
Schedule Of Pension And Other Retirement Benefits Changes In Benefit Obligation And Fair Value Of Plan Assets [Line Items]
Balance	0
Level 1 | Equity Securities
Schedule Of Pension And Other Retirement Benefits Changes In Benefit Obligation And Fair Value Of Plan Assets [Line Items]
Balance	14.6	13.3
Level 1 | Equity Securities | U.S. Large-Cap
Schedule Of Pension And Other Retirement Benefits Changes In Benefit Obligation And Fair Value Of Plan Assets [Line Items]
Balance	0
Level 1 | Equity Securities | U.S. Small And Mid-Cap
Schedule Of Pension And Other Retirement Benefits Changes In Benefit Obligation And Fair Value Of Plan Assets [Line Items]
Balance	0
Level 1 | Equity Securities | International
Schedule Of Pension And Other Retirement Benefits Changes In Benefit Obligation And Fair Value Of Plan Assets [Line Items]
Balance	0
Level 1 | Fixed Income Securities
Schedule Of Pension And Other Retirement Benefits Changes In Benefit Obligation And Fair Value Of Plan Assets [Line Items]
Balance	0
Level 1 | Fixed Income Securities | Long-term government/treasury bonds
Schedule Of Pension And Other Retirement Benefits Changes In Benefit Obligation And Fair Value Of Plan Assets [Line Items]
Balance	0
Level 1 | Fixed Income Securities | Long-term investment grade corporate bonds
Schedule Of Pension And Other Retirement Benefits Changes In Benefit Obligation And Fair Value Of Plan Assets [Line Items]
Balance	0
Level 1 | Fixed Income Securities | U.S. Treasury Inflation-Protected Securities (TIPs)
Schedule Of Pension And Other Retirement Benefits Changes In Benefit Obligation And Fair Value Of Plan Assets [Line Items]
Balance	0
Level 1 | Fixed Income Securities | Emerging Markets Bonds
Schedule Of Pension And Other Retirement Benefits Changes In Benefit Obligation And Fair Value Of Plan Assets [Line Items]
Balance	0
Level 1 | Fixed Income Securities | High Yield Bonds
Schedule Of Pension And Other Retirement Benefits Changes In Benefit Obligation And Fair Value Of Plan Assets [Line Items]
Balance	0
Level 1 | Total Other Investment
Schedule Of Pension And Other Retirement Benefits Changes In Benefit Obligation And Fair Value Of Plan Assets [Line Items]
Balance	0
Level 2
Schedule Of Pension And Other Retirement Benefits Changes In Benefit Obligation And Fair Value Of Plan Assets [Line Items]
Balance	174.4	142.2
Level 2 | Cash and Cash Equivalents
Schedule Of Pension And Other Retirement Benefits Changes In Benefit Obligation And Fair Value Of Plan Assets [Line Items]
Balance	0.4	0.2
Level 2 | Emerging Markets Equity Fund
Schedule Of Pension And Other Retirement Benefits Changes In Benefit Obligation And Fair Value Of Plan Assets [Line Items]
Balance	0
Level 2 | Common/Collective Trust Funds - Convertible Securities
Schedule Of Pension And Other Retirement Benefits Changes In Benefit Obligation And Fair Value Of Plan Assets [Line Items]
Balance	6.3	4.8
Level 2 | Private Real Estate Fund
Schedule Of Pension And Other Retirement Benefits Changes In Benefit Obligation And Fair Value Of Plan Assets [Line Items]
Balance	0
Level 2 | Equity Securities
Schedule Of Pension And Other Retirement Benefits Changes In Benefit Obligation And Fair Value Of Plan Assets [Line Items]
Balance	118.0	86.8
Level 2 | Equity Securities | U.S. Large-Cap
Schedule Of Pension And Other Retirement Benefits Changes In Benefit Obligation And Fair Value Of Plan Assets [Line Items]
Balance	44.5	32.0
Level 2 | Equity Securities | U.S. Small And Mid-Cap
Schedule Of Pension And Other Retirement Benefits Changes In Benefit Obligation And Fair Value Of Plan Assets [Line Items]
Balance	15.3	10.7
Level 2 | Equity Securities | International
Schedule Of Pension And Other Retirement Benefits Changes In Benefit Obligation And Fair Value Of Plan Assets [Line Items]
Balance	58.2	44.1
Level 2 | Fixed Income Securities
Schedule Of Pension And Other Retirement Benefits Changes In Benefit Obligation And Fair Value Of Plan Assets [Line Items]
Balance	49.7	50.4
Level 2 | Fixed Income Securities | Long-term government/treasury bonds
Schedule Of Pension And Other Retirement Benefits Changes In Benefit Obligation And Fair Value Of Plan Assets [Line Items]
Balance	13.7	13.8
Level 2 | Fixed Income Securities | Long-term investment grade corporate bonds
Schedule Of Pension And Other Retirement Benefits Changes In Benefit Obligation And Fair Value Of Plan Assets [Line Items]
Balance	15.4	17.5
Level 2 | Fixed Income Securities | U.S. Treasury Inflation-Protected Securities (TIPs)
Schedule Of Pension And Other Retirement Benefits Changes In Benefit Obligation And Fair Value Of Plan Assets [Line Items]
Balance	8.7	8.5
Level 2 | Fixed Income Securities | Emerging Markets Bonds
Schedule Of Pension And Other Retirement Benefits Changes In Benefit Obligation And Fair Value Of Plan Assets [Line Items]
Balance	5.8	5.4
Level 2 | Fixed Income Securities | High Yield Bonds
Schedule Of Pension And Other Retirement Benefits Changes In Benefit Obligation And Fair Value Of Plan Assets [Line Items]
Balance	6.1	5.2
Level 2 | Total Other Investment
Schedule Of Pension And Other Retirement Benefits Changes In Benefit Obligation And Fair Value Of Plan Assets [Line Items]
Balance	6.3	4.8
Level 3
Schedule Of Pension And Other Retirement Benefits Changes In Benefit Obligation And Fair Value Of Plan Assets [Line Items]
Balance	15.6	12.1
Level 3 | Cash and Cash Equivalents
Schedule Of Pension And Other Retirement Benefits Changes In Benefit Obligation And Fair Value Of Plan Assets [Line Items]
Balance	0
Level 3 | Emerging Markets Equity Fund
Schedule Of Pension And Other Retirement Benefits Changes In Benefit Obligation And Fair Value Of Plan Assets [Line Items]
Balance	0
Level 3 | Common/Collective Trust Funds - Convertible Securities
Schedule Of Pension And Other Retirement Benefits Changes In Benefit Obligation And Fair Value Of Plan Assets [Line Items]
Balance	0
Level 3 | Private Real Estate Fund
Schedule Of Pension And Other Retirement Benefits Changes In Benefit Obligation And Fair Value Of Plan Assets [Line Items]
Balance	15.6	12.1
Level 3 | Equity Securities
Schedule Of Pension And Other Retirement Benefits Changes In Benefit Obligation And Fair Value Of Plan Assets [Line Items]
Balance	0
Level 3 | Equity Securities | U.S. Large-Cap
Schedule Of Pension And Other Retirement Benefits Changes In Benefit Obligation And Fair Value Of Plan Assets [Line Items]
Balance	0
Level 3 | Equity Securities | U.S. Small And Mid-Cap
Schedule Of Pension And Other Retirement Benefits Changes In Benefit Obligation And Fair Value Of Plan Assets [Line Items]
Balance	0
Level 3 | Equity Securities | International
Schedule Of Pension And Other Retirement Benefits Changes In Benefit Obligation And Fair Value Of Plan Assets [Line Items]
Balance	0
Level 3 | Fixed Income Securities
Schedule Of Pension And Other Retirement Benefits Changes In Benefit Obligation And Fair Value Of Plan Assets [Line Items]
Balance	0
Level 3 | Fixed Income Securities | Long-term government/treasury bonds
Schedule Of Pension And Other Retirement Benefits Changes In Benefit Obligation And Fair Value Of Plan Assets [Line Items]
Balance	0
Level 3 | Fixed Income Securities | Long-term investment grade corporate bonds
Schedule Of Pension And Other Retirement Benefits Changes In Benefit Obligation And Fair Value Of Plan Assets [Line Items]
Balance	0
Level 3 | Fixed Income Securities | U.S. Treasury Inflation-Protected Securities (TIPs)
Schedule Of Pension And Other Retirement Benefits Changes In Benefit Obligation And Fair Value Of Plan Assets [Line Items]
Balance	0
Level 3 | Fixed Income Securities | Emerging Markets Bonds
Schedule Of Pension And Other Retirement Benefits Changes In Benefit Obligation And Fair Value Of Plan Assets [Line Items]
Balance	0
Level 3 | Fixed Income Securities | High Yield Bonds
Schedule Of Pension And Other Retirement Benefits Changes In Benefit Obligation And Fair Value Of Plan Assets [Line Items]
Balance	0
Level 3 | Total Other Investment
Schedule Of Pension And Other Retirement Benefits Changes In Benefit Obligation And Fair Value Of Plan Assets [Line Items]
Balance	$ 15.6	$ 12.1