Derivatives and Fair Value Measurements - Location and Amount of Gains and Losses on Derivatives Designated as Hedging Instruments Reported in Condensed Consolidated Statements of Comprehensive Income (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Derivatives designated as hedging instruments under ASC 815 [Member] | Interest Rate Swap [Member] | Interest and Other Expense on Debt [Member]
Derivative Instruments Gain Loss [Line Items]
Amount of Gain/(Loss) Reclassified from Accumulated Other Comprehensive Income into Income	$ 0.1	$ (0.3)	$ 0.1	$ (0.4)