Fair Values of Assets and Liabilities (Summary Of Carrying Amounts And Estimated Fair Values Of Financial Instruments) (Detail) - USD ($) $ in Thousands	Jun. 30, 2023	Dec. 31, 2022	Jun. 30, 2022
Financial Assets:
Interest-bearing deposits with banks	$ 2,163,708	$ 1,988,719	$ 3,266,541
Available-for-sale securities	3,492,481	3,243,017	2,970,121
Held-to-maturity securities	2,887,891	2,949,821	2,900,269
Equity securities with readily determinable fair value	116,275	110,365	93,295
FHLB and FRB stock, at cost	195,117	224,759	136,138
Brokerage customer receivables	15,722	16,387	21,527
Mortgage loans held-for-sale, at fair value	338,728	299,935	513,232
Accrued interest receivable and other	1,455,748	1,391,342	1,112,697
Financial Liabilities
FHLB advances	2,026,071	2,316,071	1,166,071
Other borrowings	665,219	596,614	482,787
Subordinated notes	437,628	437,392	437,162
Junior subordinated debentures	253,566	253,566	253,566
Carrying Value
Financial Assets:
Cash and cash equivalents	513,917	490,966	498,947
Securities sold under agreements to repurchase with original maturities exceeding three months	0	0	475,000
Interest-bearing deposits with banks	2,163,708	1,988,719	3,266,541
Available-for-sale securities	3,492,481	3,243,017	2,970,121
Held-to-maturity securities	3,564,473	3,640,567	3,413,469
Trading account securities	3,027	1,127	1,010
Equity securities with readily determinable fair value	116,275	110,365	93,295
FHLB and FRB stock, at cost	195,117	224,759	136,138
Brokerage customer receivables	15,722	16,387	21,527
Mortgage loans held-for-sale, at fair value	338,728	299,935	513,232
Nonqualified deferred compensation assets	14,796	13,899	13,936
Derivative assets	294,748	296,848	183,925
Accrued interest receivable and other	434,553	379,719	283,626
Total	52,170,953	49,902,793	48,923,870
Financial Liabilities
Non-maturity deposits	37,682,437	38,167,409	38,917,105
Deposits with stated maturities	6,356,270	4,735,135	3,676,221
FHLB advances	2,026,071	2,316,071	1,166,071
Other borrowings	665,219	596,614	482,787
Subordinated notes	437,628	437,392	437,162
Junior subordinated debentures	253,566	253,566	253,566
Derivative liabilities	391,172	338,078	167,857
Accrued interest payable	45,359	22,176	8,233
Total financial liabilities	47,857,722	46,866,441	45,109,002
Carrying Value | Loans held-for-investment, at fair value
Financial Assets:
Loans held-for-investment	193,953	179,932	122,757
Carrying Value | Loans held-for-investment, at amortized cost
Financial Assets:
Loans held-for-investment	40,829,455	39,016,553	36,930,346
Fair Value
Financial Assets:
Cash and cash equivalents	513,917	490,966	498,947
Securities sold under agreements to repurchase with original maturities exceeding three months	0	0	475,000
Interest-bearing deposits with banks	2,163,708	1,988,719	3,266,541
Available-for-sale securities	3,492,481	3,243,017	2,970,121
Held-to-maturity securities	2,887,891	2,949,821	2,900,269
Trading account securities	3,027	1,127	1,010
Equity securities with readily determinable fair value	116,275	110,365	93,295
FHLB and FRB stock, at cost	195,117	224,759	136,138
Brokerage customer receivables	15,722	16,387	21,527
Mortgage loans held-for-sale, at fair value	338,728	299,935	513,232
Nonqualified deferred compensation assets	14,796	13,899	13,936
Derivative assets	294,748	296,848	183,925
Accrued interest receivable and other	434,553	379,719	283,626
Total	50,807,892	48,214,172	47,646,162
Financial Liabilities
Non-maturity deposits	37,682,437	38,167,409	38,917,105
Deposits with stated maturities	6,300,161	4,085,058	3,683,452
FHLB advances	2,072,317	2,219,983	1,116,429
Other borrowings	662,156	569,342	483,592
Subordinated notes	405,762	409,395	434,809
Junior subordinated debentures	253,562	253,405	281,085
Derivative liabilities	391,172	338,078	167,857
Accrued interest payable	45,359	22,176	8,233
Total financial liabilities	47,812,926	46,064,846	45,092,562
Fair Value | Loans held-for-investment, at fair value
Financial Assets:
Loans held-for-investment	193,953	179,932	122,757
Fair Value | Loans held-for-investment, at amortized cost
Financial Assets:
Loans held-for-investment	$ 40,142,976	$ 38,018,678	$ 36,165,838