Fixed Assets, Net - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Property, Plant and Equipment [Line Items]
Depreciation expense	$ 3.2	$ 3.0
Software development costs capitalized	0.5	0.1
Operating, Administrative and Other [Member]
Property, Plant and Equipment [Line Items]
Amortization of software development costs	$ 0.2	$ 0.1