Pension and Post-retirement Benefit Plans - Schedule of Pension Plan Assets at Fair Value (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Pension And Other Employee Benefit Plans [Line Items]
Fair value of pension plan assets	$ 175.6	$ 146.6
U.S. equity securities [Member]
Pension And Other Employee Benefit Plans [Line Items]
Fair value of pension plan assets	80.0	71.8
International equity securities [Member]
Pension And Other Employee Benefit Plans [Line Items]
Fair value of pension plan assets	27.2	22.6
U.S. debt securities [Member]
Pension And Other Employee Benefit Plans [Line Items]
Fair value of pension plan assets	36.4	22.0
International debt securities [Member]
Pension And Other Employee Benefit Plans [Line Items]
Fair value of pension plan assets	24.5	22.4
Real estate and other investments [Member]
Pension And Other Employee Benefit Plans [Line Items]
Fair value of pension plan assets	1.7	1.6
Cash & cash equivalents [Member]
Pension And Other Employee Benefit Plans [Line Items]
Fair value of pension plan assets	5.8	6.2
Quoted prices in active markets for identical assets (Level 1) [Member]
Pension And Other Employee Benefit Plans [Line Items]
Fair value of pension plan assets	0	0
Quoted prices in active markets for identical assets (Level 1) [Member] | U.S. equity securities [Member]
Pension And Other Employee Benefit Plans [Line Items]
Fair value of pension plan assets	0	0
Quoted prices in active markets for identical assets (Level 1) [Member] | International equity securities [Member]
Pension And Other Employee Benefit Plans [Line Items]
Fair value of pension plan assets	0	0
Quoted prices in active markets for identical assets (Level 1) [Member] | U.S. debt securities [Member]
Pension And Other Employee Benefit Plans [Line Items]
Fair value of pension plan assets	0	0
Quoted prices in active markets for identical assets (Level 1) [Member] | International debt securities [Member]
Pension And Other Employee Benefit Plans [Line Items]
Fair value of pension plan assets	0	0
Quoted prices in active markets for identical assets (Level 1) [Member] | Real estate and other investments [Member]
Pension And Other Employee Benefit Plans [Line Items]
Fair value of pension plan assets	0	0
Quoted prices in active markets for identical assets (Level 1) [Member] | Cash & cash equivalents [Member]
Pension And Other Employee Benefit Plans [Line Items]
Fair value of pension plan assets	0	0
Significant observable inputs (Level 2) [Member]
Pension And Other Employee Benefit Plans [Line Items]
Fair value of pension plan assets	175.6	146.6
Significant observable inputs (Level 2) [Member] | U.S. equity securities [Member]
Pension And Other Employee Benefit Plans [Line Items]
Fair value of pension plan assets	80.0	71.8
Significant observable inputs (Level 2) [Member] | International equity securities [Member]
Pension And Other Employee Benefit Plans [Line Items]
Fair value of pension plan assets	27.2	22.6
Significant observable inputs (Level 2) [Member] | U.S. debt securities [Member]
Pension And Other Employee Benefit Plans [Line Items]
Fair value of pension plan assets	36.4	22.0
Significant observable inputs (Level 2) [Member] | International debt securities [Member]
Pension And Other Employee Benefit Plans [Line Items]
Fair value of pension plan assets	24.5	22.4
Significant observable inputs (Level 2) [Member] | Real estate and other investments [Member]
Pension And Other Employee Benefit Plans [Line Items]
Fair value of pension plan assets	1.7	1.6
Significant observable inputs (Level 2) [Member] | Cash & cash equivalents [Member]
Pension And Other Employee Benefit Plans [Line Items]
Fair value of pension plan assets	5.8	6.2
Significant unobservable inputs (Level 3) [Member]
Pension And Other Employee Benefit Plans [Line Items]
Fair value of pension plan assets	0	0
Significant unobservable inputs (Level 3) [Member] | U.S. equity securities [Member]
Pension And Other Employee Benefit Plans [Line Items]
Fair value of pension plan assets	0	0
Significant unobservable inputs (Level 3) [Member] | International equity securities [Member]
Pension And Other Employee Benefit Plans [Line Items]
Fair value of pension plan assets	0	0
Significant unobservable inputs (Level 3) [Member] | U.S. debt securities [Member]
Pension And Other Employee Benefit Plans [Line Items]
Fair value of pension plan assets	0	0
Significant unobservable inputs (Level 3) [Member] | International debt securities [Member]
Pension And Other Employee Benefit Plans [Line Items]
Fair value of pension plan assets	0	0
Significant unobservable inputs (Level 3) [Member] | Real estate and other investments [Member]
Pension And Other Employee Benefit Plans [Line Items]
Fair value of pension plan assets	0	0
Significant unobservable inputs (Level 3) [Member] | Cash & cash equivalents [Member]
Pension And Other Employee Benefit Plans [Line Items]
Fair value of pension plan assets	$ 0	$ 0