Derivative Instruments and Hedging Activities - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Derivative [Line Items]
Notional amount	$ 6,942,000,000	$ 5,628,000,000
Additional amount in excess of posted collateral required in case of breached agreements	$ 700,000	900,000
Interest Rate Contracts
Derivative [Line Items]
Maximum length of time hedged in interest rate cash flow hedge	6 years
Period to reclassification of cash flow hedge gain loss	12 months
Derivative gains to be reclassified within twelve months	$ 3,400,000
Derivative gains to be reclassified within twelve months, net of tax	2,700,000
Hedge ineffectiveness	0	0
Gains or losses from cash flow hedge derivatives reclassified to earnings	$ 0	0
Interest Rate Lock Commitments | Minimum
Derivative [Line Items]
Lock in period for interest rates	30 days
Interest Rate Lock Commitments | Maximum
Derivative [Line Items]
Lock in period for interest rates	270 days
Credit Risk Contracts
Derivative [Line Items]
Notional amount	$ 140,600,000
Maximum exposure under credit risk agreement assuming customer default	100,000	100,000
Credit risk derivatives, purchased at fair value	0	40,000
Credit risk derivatives, sold at fair value	$ (110,000)	$ (100,000)
Credit Risk Contracts | Minimum
Derivative [Line Items]
Risk participation agreements, term	9 months
Credit Risk Contracts | Maximum
Derivative [Line Items]
Risk participation agreements, term	10 years