Derivative Financial Instruments (Narrative) (Detail)	3 Months Ended		9 Months Ended
	Sep. 30, 2017 USD ($) derivative_instruments	Sep. 30, 2016 USD ($) derivative_instruments	Sep. 30, 2017 USD ($) derivative_instruments	Sep. 30, 2016 USD ($) derivative_instruments	Dec. 31, 2016 derivative_instruments
Derivative Instruments, Gain (Loss) [Line Items]
Amount reclassified from accumulated other comprehensive income to interest expense in the next twelve months			$ 3,500,000
Net derivative liability position, aggregate fair value	$ 9,800,000		9,800,000
Interest Rate Contract | Not Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount	4,900,000,000		4,900,000,000
Forward Commitments to Sell Mortgage Loans | Not Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount	773,500,000		773,500,000
Interest Rate Lock Commitments | Not Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount	409,300,000		409,300,000
Foreign Exchange Contract | Not Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount	$ 43,400,000		$ 43,400,000
Covered Call Options | Not Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Number of derivative instruments held | derivative_instruments	0	0	0	0	0
Cash Flow Hedging | Interest Rate Contract | Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on cash flow hedge ineffectiveness, net			$ 0	$ 0
Cash Flow Hedging | Cash flow hedge of variable rate deposits | Interest Rate Swap | Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Number of interest rate derivatives held | derivative_instruments	4		4
Cash Flow Hedging | Interest Rate Swap, $200 million, June 2019 | Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount	$ 200,000,000		$ 200,000,000
Cash Flow Hedging | Interest Rate Swap, $200 million, June 2019 | Interest Rate Swap | Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount	200,000,000		200,000,000
Cash Flow Hedging | Interest Rate Swap, $250 million, July 2019 | Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount	250,000,000		250,000,000
Cash Flow Hedging | Interest Rate Swap, $250 million, July 2019 | Interest Rate Swap | Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount	250,000,000.0		250,000,000.0
Cash Flow Hedging | Interest Rate Swap, $275 million, August 2019 | Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount	275,000,000		275,000,000
Cash Flow Hedging | Interest Rate Swap, $275 million, August 2019 | Interest Rate Swap | Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount	275,000,000.0		275,000,000.0
Cash Flow Hedging | Interest Rate Swap, $200 million, June 2020 | Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount	200,000,000		200,000,000
Cash Flow Hedging | Interest Rate Swap, $200 million, June 2020 | Interest Rate Swap | Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount	$ 200,000,000.0		$ 200,000,000.0
Fair Value Hedging | Interest Rate Swap | Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Number of interest rate derivatives held | derivative_instruments	11		11
Notional amount	$ 126,100,000		$ 126,100,000
Fair Value Hedging | Interest Rate Contract | Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on fair value hedge ineffectiveness, net	$ 12,000	$ 35,000	$ 41,000	$ 13,000