Derivative Instruments and Hedging Activities - Additional Information (Detail) $ in Millions	9 Months Ended
	Sep. 30, 2016 USD ($) Derivative Swap	Dec. 31, 2015 USD ($) Derivative Swap
Derivative Instruments, Gain (Loss) [Line Items]
Reclassification adjustment from accumulated other comprehensive income	$ 2.4
Assets needed for immediate settlement of derivatives in a net liability position	26.5
Minimum collateral with counterparties	$ 27.7
Minimum
Derivative Instruments, Gain (Loss) [Line Items]
Derivative expiration period	30 days
Maximum
Derivative Instruments, Gain (Loss) [Line Items]
Derivative expiration period	60 days
Not Designated as Hedging Instrument | Residential mortgage loan commitments
Derivative Instruments, Gain (Loss) [Line Items]
Aggregate notional amount	$ 5.2	$ 2.8
Interest Rate Swaps | Derivative Designated as Cash Flow Hedges | Cash Flow Hedges
Derivative Instruments, Gain (Loss) [Line Items]
Number of outstanding interest rate derivatives (derivative) | Derivative	1	1
Aggregate notional amount	$ 150.0	$ 150.0
Interest Rate Swaps | Not Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Aggregate notional amount	$ 701.7	$ 461.0
Number of interest rate swaps (swap) | Swap	74	62
Credit Contract | Not Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Aggregate notional amount	$ 35.7	$ 19.3