Derivative Financial Instruments - Customer-related derivative positions (Detail) - Not Designated as Hedging Instrument $ in Thousands	Mar. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)
Interest rate swaps
Disclosure Of Customer Related Derivatives Not Designated As Hedging [Line Items]
Number of Positions	562	576
Total Notional	$ 3,571,918	$ 3,652,385
Risk participation agreements
Disclosure Of Customer Related Derivatives Not Designated As Hedging [Line Items]
Number of Positions	70	70
Total Notional	$ 288,803	$ 287,732
Matched commercial customer book
Disclosure Of Customer Related Derivatives Not Designated As Hedging [Line Items]
Number of Positions	74	40
Total Notional	$ 8,428	$ 4,242
Foreign currency loan
Disclosure Of Customer Related Derivatives Not Designated As Hedging [Line Items]
Number of Positions	3	3
Total Notional	$ 7,988	$ 10,798