Property and Equipment - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Property, Plant and Equipment [Line Items]
Depreciation expense, including amortization capitalized software development costs	$ 2.8	$ 2.1
Software and Development Costs
Property, Plant and Equipment [Line Items]
Capitalized software development costs	3.4
Amortization expense	1.9	1.5
Unamortized software development costs	$ 19.3