Acquisitions (Change in contingent purchase price liability related to prior acquisitions) - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Business Combinations [Abstract]
Fair value of contingent consideration	$ 0.0	$ 2.1	$ 1.5	$ 3.0