Amortization Expense Relating to Acquired Intangible Assets (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Finite Lived Intangible Assets [Line Items]
Amortization expense	$ 31.9	$ 28.4	$ 28.0