Fair Value Measurements - Estimated Fair Value of Financial Instruments (Detail) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and short-term investments	$ 4,258,984	$ 2,638,384
Securities available for sale	6,330,699	7,006,347
Securities held to maturity (exclusive of allowance for credit losses)	5,732,583	5,861,599
Trading securities	24,509	17,980
Other securities	473,255	349,758
Loans (exclusive of allowance for credit losses)	22,884,513	21,033,167
Derivatives	144,310	48,121
Demand and savings deposits	30,088,499	31,721,995
Time deposits	3,343,253	917,138
Other borrowings	4,057,602	2,222,167
Long-term debt	382,768	381,311
Derivatives	151,527	126,334
Estimate of Fair Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and short-term investments	4,258,984	2,638,384
Securities available for sale	6,330,699	7,006,347
Securities held to maturity (exclusive of allowance for credit losses)	4,856,466	5,280,659
Trading securities	24,509	17,980
Other securities	473,255	349,758
Loans (exclusive of allowance for credit losses)		20,816,899
Derivatives	144,310	48,121
Demand and savings deposits	30,088,499	31,721,995
Time deposits		917,138
Other borrowings	4,057,602	2,222,167
Long-term debt		418,737
Derivatives	151,527	126,334
Commitments to extend credit for loans	8,250	9,260
Commitments to extend resell agreements	83
Commercial letters of credit	83	185
Standby letters of credit	3,112	3,982
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and short-term investments	4,012,781	1,686,787
Securities available for sale	1,124,276	1,144,570
Trading securities	9,191	2,384
Other securities	10,780	10,782
Demand and savings deposits	30,088,499	31,721,995
Other borrowings	49,213	62,480
Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and short-term investments	246,203	951,597
Securities available for sale	5,206,423	5,861,777
Securities held to maturity (exclusive of allowance for credit losses)	4,856,466	5,280,659
Trading securities	15,318	15,596
Other securities	462,475	338,976
Loans (exclusive of allowance for credit losses)		20,816,899
Derivatives	144,310	48,121
Time deposits		917,138
Other borrowings		2,159,687
Long-term debt		418,737
Derivatives	$ 151,527	$ 126,334