Operating Leases - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Operating Leased Assets [Line Items]
Net rental expense	$ 20.0	$ 18.2	$ 14.7
Sublease rentals	$ 0.1	$ 0.3	$ 0.2
Minimum
Operating Leased Assets [Line Items]
Operating leases term, in years	1 year
Maximum
Operating Leased Assets [Line Items]
Operating leases term, in years	15 years