Fair Value Measurements - Estimated Fair Value of Financial Instruments (Detail) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and short-term investments	$ 8,033,522	$ 10,472,084
Securities available for sale	8,550,093	11,976,514
Total held to maturity securities	4,602,232	1,480,416
Trading securities	17,059	31,875
Other securities	332,123	327,098
Loans (exclusive of allowance for credit losses)	17,732,083	17,172,148
Derivatives	19,973	57,680
Demand and savings deposits	33,775,532	34,748,286
Time deposits	587,033	851,641
Other borrowings	2,840,535	3,238,435
Long-term debt	272,036	271,544
Derivatives	43,016	13,944
Estimate of Fair Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and short-term investments	8,033,522	10,472,084
Securities available for sale	8,550,093	11,976,514
Total held to maturity securities	4,393,455	1,442,391
Trading securities	17,059	31,875
Other securities	332,123	327,098
Loans (exclusive of allowance for credit losses)	17,820,959	17,506,662
Derivatives	19,973	57,680
Demand and savings deposits	33,775,532	34,748,286
Time deposits	587,033	851,641
Other borrowings	2,840,535	3,238,435
Long-term debt	278,844	285,961
Derivatives	43,016	13,944
Commitments to extend credit for loans	2,167	7,841
Commercial letters of credit	47	179
Standby letters of credit	924	3,553
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	6,715,213	9,255,727
Securities available for sale	748,220	387,020
Trading securities	1,585	5,985
Other securities	53,056	64,149
Demand and savings deposits	33,775,532	34,748,286
Other borrowings	85,791	12,597
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	1,318,309	1,216,357
Securities available for sale	7,801,873	11,589,494
Total held to maturity securities	4,393,455	1,442,391
Trading securities	15,474	25,890
Other securities	279,067	262,949
Loans (exclusive of allowance for credit losses)	17,820,959	17,506,662
Derivatives	19,973	57,680
Time deposits	587,033	851,641
Other borrowings	2,754,744	3,225,838
Long-term debt	278,844	285,961
Derivatives	$ 43,016	$ 13,944