Property and Equipment, Net - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Property, Plant and Equipment [Abstract]
Depreciation and amortization expense related to property and equipment	$ 3.0	$ 2.5	$ 9.0	$ 7.1
Property and equipment under capital lease	3.2		3.2		3.2
Accumulated depreciation related to assets under capital lease	2.5		2.5		2.1
Internal-use software development costs capitalized	0	1.5	0	6.6
Carrying value of internal-use software, net of accumulated amortization	9.8		9.8		13.6
Amortization of capitalized costs related to internal-use software	$ 1.3	$ 0.8	$ 3.8	$ 2.1