Fair Values of Assets and Liabilities (Summary Of Carrying Amounts And Estimated Fair Values Of Financial Instruments) (Detail) - USD ($) $ in Thousands	Sep. 30, 2022	Dec. 31, 2021	Sep. 30, 2021
Financial Assets:
Interest-bearing deposits with banks	$ 3,968,605	$ 5,372,603	$ 5,232,315
Available-for-sale securities	2,923,653	2,327,793	2,373,478
Held-to-maturity securities	2,679,326	2,900,694	2,699,480
Equity securities with readily determinable fair value	114,012	90,511	88,193
FHLB and FRB stock, at cost	178,156	135,378	135,408
Brokerage customer receivables	20,327	26,068	26,378
Mortgage loans held-for-sale, at fair value	376,160	817,912	925,312
Accrued interest receivable and other	1,316,305	1,084,115	1,166,917
Financial Liabilities
FHLB advances	2,316,071	1,241,071	1,241,071
Other borrowings	447,215	494,136	504,527
Subordinated notes	437,260	436,938	436,811
Junior subordinated debentures	253,566	253,566	253,566
Carrying Value
Financial Assets:
Cash and cash equivalents	489,647	411,205	462,299
Securities sold under agreements to repurchase with original maturities exceeding three months	0	700,000	0
Interest-bearing deposits with banks	3,968,605	5,372,603	5,232,315
Available-for-sale securities	2,923,653	2,327,793	2,373,478
Held-to-maturity securities	3,389,842	2,942,285	2,736,722
Trading account securities	179	1,061	1,103
Equity securities with readily determinable fair value	114,012	90,511	88,193
FHLB and FRB stock, at cost	178,156	135,378	135,408
Brokerage customer receivables	20,327	26,068	26,378
Mortgage loans held-for-sale, at fair value	376,160	817,912	925,312
Nonqualified deferred compensation assets	13,387	16,240	15,797
Derivative assets	313,480	165,008	191,612
Accrued interest receivable and other	317,142	268,921	272,293
Total	50,272,203	48,064,089	45,724,953
Financial Liabilities
Non-maturity deposits	38,720,873	38,126,796	35,822,012
Deposits with stated maturities	4,076,318	3,968,789	4,130,546
FHLB advances	2,316,071	1,241,071	1,241,071
Other borrowings	447,215	494,136	504,527
Subordinated notes	437,260	436,938	436,811
Junior subordinated debentures	253,566	253,566	253,566
Derivative liabilities	357,170	123,000	161,314
Accrued interest payable	18,479	9,304	15,030
Total financial liabilities	46,626,952	44,653,600	42,564,877
Carrying Value | Loans held-for-investment, at fair value
Financial Assets:
Loans held-for-investment	156,893	38,598	30,979
Carrying Value | Loans held-for-investment, at amortized cost
Financial Assets:
Loans held-for-investment	38,010,720	34,750,506	33,233,064
Fair Value
Financial Assets:
Cash and cash equivalents	489,647	411,205	462,299
Securities sold under agreements to repurchase with original maturities exceeding three months	0	700,000	0
Interest-bearing deposits with banks	3,968,605	5,372,603	5,232,315
Available-for-sale securities	2,923,653	2,327,793	2,373,478
Held-to-maturity securities	2,679,326	2,900,694	2,699,480
Trading account securities	179	1,061	1,103
Equity securities with readily determinable fair value	114,012	90,511	88,193
FHLB and FRB stock, at cost	178,156	135,378	135,408
Brokerage customer receivables	20,327	26,068	26,378
Mortgage loans held-for-sale, at fair value	376,160	817,912	925,312
Nonqualified deferred compensation assets	13,387	16,240	15,797
Derivative assets	313,480	165,008	191,612
Accrued interest receivable and other	317,142	268,921	272,293
Total	48,775,720	48,569,870	45,731,335
Financial Liabilities
Non-maturity deposits	38,720,873	38,126,796	35,822,012
Deposits with stated maturities	4,087,196	3,965,372	4,124,199
FHLB advances	2,230,921	1,186,280	1,164,168
Other borrowings	447,971	494,670	504,527
Subordinated notes	417,363	472,684	474,171
Junior subordinated debentures	285,238	212,226	207,675
Derivative liabilities	357,170	123,000	161,314
Accrued interest payable	18,479	9,304	15,030
Total financial liabilities	46,565,211	44,590,332	42,473,096
Fair Value | Loans held-for-investment, at fair value
Financial Assets:
Loans held-for-investment	156,893	38,598	30,979
Fair Value | Loans held-for-investment, at amortized cost
Financial Assets:
Loans held-for-investment	$ 37,224,753	$ 35,297,878	$ 33,276,688