Derivative Financial Instruments - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Derivative [Line Items]
Percentage of total notional derivative contracts	92.10%
Total amount of notional derivative contracts	$ 5,200.0
Net positive exposure	44.6	$ 50.1
Estimated reclassification of AOCI to interest expense	11.2
Cash collateral held relative to derivative exposure	1.0	1.1
Cash collateral pledged	49.1	$ 54.8
Chicago Mercantile Exchange and the London Clearing House
Derivative [Line Items]
Total amount of notional derivative contracts	$ 4,800.0