Deposits - Schedule of Deposits (Detail) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Deposit [Line Items]
Total non-interest-bearing demand deposits	$ 16,459,535	$ 15,117,051
Interest-bearing Deposit Liabilities, Total	22,274,605	19,898,710
Total deposits	$ 38,734,140	$ 35,015,761
Total non-interest-bearing demand deposits, Percentage of Total	42.50%	43.20%
Percentage of Interest-bearing Domestic Deposits to Deposits	57.50%	56.80%
Total deposits, Percentage of Total	100.00%	100.00%
Commercial and Individual [Member]
Deposit [Line Items]
Total non-interest-bearing demand deposits	$ 15,455,094	$ 13,914,754
Total non-interest-bearing demand deposits, Percentage of Total	39.90%	39.70%
Correspondent Banks [Member]
Deposit [Line Items]
Total non-interest-bearing demand deposits	$ 192,050	$ 242,225
Total non-interest-bearing demand deposits, Percentage of Total	0.50%	0.70%
Private Accounts [Member]
Deposit [Line Items]
Savings and interest checking	$ 10,728,710	$ 9,132,789
Money market accounts	9,739,422	8,977,585
Time Deposits	1,117,883	1,135,575
Interest-bearing Deposit Liabilities, Total	$ 21,586,015	$ 19,245,949
Savings and interest checking, Percentage of Total	27.70%	26.10%
Money market accounts, Percentage of Total	25.10%	25.60%
Percentage Of Time Accounts To Deposits	2.90%	3.30%
Percentage of Interest-bearing Domestic Deposits to Deposits	55.70%	55.00%
Public Funds [Member]
Deposit [Line Items]
Total non-interest-bearing demand deposits	$ 812,391	$ 960,072
Savings and interest checking	611,123	597,503
Money market accounts	61,360	50,070
Time Deposits	16,107	5,188
Interest-bearing Deposit Liabilities, Total	$ 688,590	$ 652,761
Total non-interest-bearing demand deposits, Percentage of Total	2.10%	2.80%
Savings and interest checking, Percentage of Total	1.60%	1.70%
Money market accounts, Percentage of Total	0.20%	0.10%
Percentage Of Time Accounts To Deposits	0.00%	0.00%
Percentage of Interest-bearing Domestic Deposits to Deposits	1.80%	1.80%