Goodwill and Intangible Assets - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Goodwill and Intangible Assets Disclosure [Line Items]
Amortization expense on identifiable intangible assets	$ 29.1	$ 25.0	$ 21.5
Expected amortization expenses in year one	30.0
Expected amortization expenses in year two	30.0
Expected amortization expenses in year three	30.0
Expected amortization expenses in year four	30.0
Expected amortization expenses in year five	30.0
Accumulated goodwill impairment loss	$ 369.3	$ 369.3