Goodwill and Intangible Assets - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Goodwill and Intangible Assets Disclosure [Line Items]
Amortization expense for intangible assets	$ 0.9	$ 0.6
Estimated amortization expense for the remainder of 2013	2.2
Estimated amortization expense for 2014	4.2
Estimated amortization expense for 2015	4.8
Estimated amortization expense for 2016	4.9
Estimated amortization expense for 2017	$ 4.7