Goodwill and Other Intangible Assets - Summary of Goodwill and Other Intangible Assets (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Finite-Lived Intangible Assets [Line Items]
Goodwill	$ 18.1	$ 18.1	$ 18.1	$ 18.1
Accumulated Impairments	(11.8)	(11.8)	(11.8)	(11.8)
Goodwill, Net	6.3	6.3	$ 6.3	$ 6.3
Customer relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Cost amortizable intangible assets	1.4	1.4
Accumulated amortization intangible assets	$ 0.9	$ 0.8