Commitments and Contingencies (Outstanding Financial Instruments Contract Amounts Represent Credit Risk) (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Loss Contingencies [Line Items]
Unused Commitments to Extend Credit	$ 6,379,941	$ 6,050,806
Standby letters of credit [Member]
Loss Contingencies [Line Items]
Unused Commitments to Extend Credit	188,103	189,040
Letter of Credit [Member]
Loss Contingencies [Line Items]
Unused Commitments to Extend Credit	29,180	21,181
Commitments to extend credit [Member]
Loss Contingencies [Line Items]
Unused Commitments to Extend Credit	$ 6,162,658	$ 5,840,585