Goodwill and Other Intangible Assets - Summary of Goodwill and Other Intangible Assets (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Finite-Lived Intangible Assets [Line Items]
Beginning Balance, Goodwill		$ 18.1	$ 18.1	$ 18.1
Ending Balance, Goodwill	18.1	18.1	18.1	18.1
Beginning Balance, Accumulated Impairments		(11.8)	(9.9)	(9.5)
Goodwill impairment	(1.9)		(1.9)	(0.4)
Ending Balance, Accumulated Impairments	(11.8)	(11.8)	(11.8)	(9.9)
Beginning Balance, Goodwill Net		6.3	8.2	8.6
Goodwill, Net			(1.9)	(0.4)
Ending Balance, Goodwill Net	6.3	6.3	6.3	8.2
Customer relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Cost amortizable intangible assets		1.4	1.4
Accumulated amortization intangible assets	$ 0.6	$ 0.7	$ 0.6