Commitments and Contingencies (Outstanding Financial Instruments Contract Amounts Represent Credit Risk) (Detail) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Loss Contingencies [Line Items]
Unused Commitments to Extend Credit	$ 7,407,777	$ 6,755,563
Standby letter of credit [Member]
Loss Contingencies [Line Items]
Unused Commitments to Extend Credit	213,751	207,201
Commercial letter of credit [Member]
Loss Contingencies [Line Items]
Unused Commitments to Extend Credit	50,120	30,522
Commitments to extend credit [Member]
Loss Contingencies [Line Items]
Unused Commitments to Extend Credit	$ 7,143,906	$ 6,517,840