Goodwill and Other Identifiable Intangible Assets - Schedule of Identifiable Intangible Assets (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 26.2	$ 17.0
Accumulated Amortization	10.9	9.0
Net	15.3	8.0
Customer contracts [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	20.9	12.3
Accumulated Amortization	8.1	6.8
Net	12.8	5.5
Supply contracts [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	2.8	2.7
Accumulated Amortization	0.8	0.5
Net	2.0	2.2
Favorable lease agreements [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	1.7	1.2
Accumulated Amortization	1.2	1.2
Net	0.5	0
Non-compete agreements [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	0.8	0.8
Accumulated Amortization	0.8	0.5
Net	$ 0	$ 0.3