Fair Values of Assets and Liabilities (Summary Of Carrying Amounts And Estimated Fair Values Of Financial Instruments) (Detail) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022	Mar. 31, 2022
Financial Assets:
Interest-bearing deposits with banks	$ 1,563,578	$ 1,988,719	$ 4,013,597
Available-for-sale securities	3,259,845	3,243,017	2,998,898
Held-to-maturity securities	2,976,198	2,949,821	3,146,427
Equity securities with readily determinable fair value	111,943	110,365	92,689
FHLB and FRB stock, at cost	244,957	224,759	136,163
Brokerage customer receivables	16,042	16,387	22,888
Mortgage loans held-for-sale, at fair value	302,493	299,935	606,545
Accrued interest receivable and other	1,413,795	1,391,342	1,066,750
Financial Liabilities
FHLB advances	2,316,071	2,316,071	1,241,071
Other borrowings	583,548	596,614	482,516
Subordinated notes	437,493	437,392	437,033
Junior subordinated debentures	253,566	253,566	253,566
Carrying Value
Financial Assets:
Cash and cash equivalents	445,986	490,966	462,572
Securities sold under agreements to repurchase with original maturities exceeding three months	0	0	700,000
Interest-bearing deposits with banks	1,563,578	1,988,719	4,013,597
Available-for-sale securities	3,259,845	3,243,017	2,998,898
Held-to-maturity securities	3,606,391	3,640,567	3,435,729
Trading account securities	102	1,127	852
Equity securities with readily determinable fair value	111,943	110,365	92,689
FHLB and FRB stock, at cost	244,957	224,759	136,163
Brokerage customer receivables	16,042	16,387	22,888
Mortgage loans held-for-sale, at fair value	302,493	299,935	606,545
Nonqualified deferred compensation assets	14,379	13,899	15,447
Derivative assets	274,004	296,848	153,534
Accrued interest receivable and other	417,066	379,719	278,873
Total	49,822,257	49,902,793	48,198,334
Financial Liabilities
Non-maturity deposits	37,366,959	38,167,409	38,483,327
Deposits with stated maturities	5,351,252	4,735,135	3,735,995
FHLB advances	2,316,071	2,316,071	1,241,071
Other borrowings	583,548	596,614	482,516
Subordinated notes	437,493	437,392	437,033
Junior subordinated debentures	253,566	253,566	253,566
Derivative liabilities	274,432	338,078	122,107
Accrued interest payable	42,015	22,176	14,269
Total financial liabilities	46,625,336	46,866,441	44,769,884
Carrying Value | Loans held-for-investment, at fair value
Financial Assets:
Loans held-for-investment	202,143	179,932	57,984
Carrying Value | Loans held-for-investment, at amortized cost
Financial Assets:
Loans held-for-investment	39,363,328	39,016,553	35,222,563
Fair Value
Financial Assets:
Cash and cash equivalents	445,986	490,966	462,572
Securities sold under agreements to repurchase with original maturities exceeding three months	0	0	700,000
Interest-bearing deposits with banks	1,563,578	1,988,719	4,013,597
Available-for-sale securities	3,259,845	3,243,017	2,998,898
Held-to-maturity securities	2,976,198	2,949,821	3,146,427
Trading account securities	102	1,127	852
Equity securities with readily determinable fair value	111,943	110,365	92,689
FHLB and FRB stock, at cost	244,957	224,759	136,163
Brokerage customer receivables	16,042	16,387	22,888
Mortgage loans held-for-sale, at fair value	302,493	299,935	606,545
Nonqualified deferred compensation assets	14,379	13,899	15,447
Derivative assets	274,004	296,848	153,534
Accrued interest receivable and other	417,066	379,719	278,873
Total	48,406,497	48,214,172	48,676,309
Financial Liabilities
Non-maturity deposits	37,366,959	38,167,409	38,483,327
Deposits with stated maturities	4,970,556	4,085,058	3,735,750
FHLB advances	2,255,580	2,219,983	1,193,080
Other borrowings	555,615	569,342	483,202
Subordinated notes	410,827	409,395	446,711
Junior subordinated debentures	252,663	253,405	268,913
Derivative liabilities	274,432	338,078	122,107
Accrued interest payable	42,015	22,176	14,269
Total financial liabilities	46,128,647	46,064,846	44,747,359
Fair Value | Loans held-for-investment, at fair value
Financial Assets:
Loans held-for-investment	202,143	179,932	57,984
Fair Value | Loans held-for-investment, at amortized cost
Financial Assets:
Loans held-for-investment	$ 38,577,761	$ 38,018,678	$ 35,989,840