Freestanding Derivative Financial Instruments - Additional Information (Detail) - USD ($) $ in Millions	Jun. 30, 2015	Dec. 31, 2014
Offsetting [Abstract]
Derivative Asset	$ 2.2	$ 0.1
Derivative Liability	12.7	$ 10.2
Net settlement liability subject to master repurchase arrangements	0.4
Derivative Liability, Collateral, Right to Reclaim Cash, Offset	(3.5)
Derivative, Fair Value, Amount Offset Against Collateral, Net	(0.6)
OverCollateralizedPositionforOffset	$ 2.5