Fair Values of Assets and Liabilities (Summary Of Carrying Amounts And Estimated Fair Values Of Financial Instruments) (Detail) - USD ($) $ in Thousands	Jun. 30, 2022	Dec. 31, 2021	Jun. 30, 2021
Financial Assets:
Interest-bearing deposits with banks	$ 3,266,541	$ 5,372,603	$ 4,707,415
Available-for-sale securities	2,970,121	2,327,793	2,188,608
Held-to-maturity securities	2,900,269	2,900,694	2,480,232
Equity securities with readily determinable fair value	93,295	90,511	86,316
FHLB and FRB stock, at cost	136,138	135,378	136,625
Brokerage customer receivables	21,527	26,068	23,093
Mortgage loans held-for-sale, at fair value	513,232	817,912	984,994
Accrued interest receivable and other	1,112,697	1,084,115	1,185,811
Financial Liabilities
FHLB advances	1,166,071	1,241,071	1,241,071
Other borrowings	482,787	494,136	518,493
Subordinated notes	437,162	436,938	436,719
Junior subordinated debentures	253,566	253,566	253,566
Carrying Value
Financial Assets:
Cash and cash equivalents	498,947	411,205	435,009
Securities sold under agreements to repurchase with original maturities exceeding three months	475,000	700,000	0
Interest-bearing deposits with banks	3,266,541	5,372,603	4,707,415
Available-for-sale securities	2,970,121	2,327,793	2,188,608
Held-to-maturity securities	3,413,469	2,942,285	2,498,232
Trading account securities	1,010	1,061	2,667
Equity securities with readily determinable fair value	93,295	90,511	86,316
FHLB and FRB stock, at cost	136,138	135,378	136,625
Brokerage customer receivables	21,527	26,068	23,093
Mortgage loans held-for-sale, at fair value	513,232	817,912	984,994
Nonqualified deferred compensation assets	13,936	16,240	16,590
Derivative assets	183,925	165,008	212,380
Accrued interest receivable and other	283,626	268,921	270,087
Total	48,923,870	48,064,089	44,473,203
Financial Liabilities
Non-maturity deposits	38,917,105	38,126,796	34,440,741
Deposits with stated maturities	3,676,221	3,968,789	4,363,875
FHLB advances	1,166,071	1,241,071	1,241,071
Other borrowings	482,787	494,136	518,493
Subordinated notes	437,162	436,938	436,719
Junior subordinated debentures	253,566	253,566	253,566
Derivative liabilities	167,857	123,000	193,439
Accrued interest payable	8,233	9,304	10,551
Total financial liabilities	45,109,002	44,653,600	41,458,455
Carrying Value | Loans held-for-investment, at fair value
Financial Assets:
Loans held-for-investment	122,757	38,598	55,340
Carrying Value | Loans held-for-investment, at amortized cost
Financial Assets:
Loans held-for-investment	36,930,346	34,750,506	32,855,847
Fair Value
Financial Assets:
Cash and cash equivalents	498,947	411,205	435,009
Securities sold under agreements to repurchase with original maturities exceeding three months	475,000	700,000	0
Interest-bearing deposits with banks	3,266,541	5,372,603	4,707,415
Available-for-sale securities	2,970,121	2,327,793	2,188,608
Held-to-maturity securities	2,900,269	2,900,694	2,480,232
Trading account securities	1,010	1,061	2,667
Equity securities with readily determinable fair value	93,295	90,511	86,316
FHLB and FRB stock, at cost	136,138	135,378	136,625
Brokerage customer receivables	21,527	26,068	23,093
Mortgage loans held-for-sale, at fair value	513,232	817,912	984,994
Nonqualified deferred compensation assets	13,936	16,240	16,590
Derivative assets	183,925	165,008	212,380
Accrued interest receivable and other	283,626	268,921	270,087
Total	47,646,162	48,569,870	44,430,761
Financial Liabilities
Non-maturity deposits	38,917,105	38,126,796	34,440,741
Deposits with stated maturities	3,683,452	3,965,372	4,352,116
FHLB advances	1,116,429	1,186,280	1,161,457
Other borrowings	483,592	494,670	518,493
Subordinated notes	434,809	472,684	476,683
Junior subordinated debentures	281,085	212,226	206,614
Derivative liabilities	167,857	123,000	193,439
Accrued interest payable	8,233	9,304	10,551
Total financial liabilities	45,092,562	44,590,332	41,360,094
Fair Value | Loans held-for-investment, at fair value
Financial Assets:
Loans held-for-investment	122,757	38,598	55,340
Fair Value | Loans held-for-investment, at amortized cost
Financial Assets:
Loans held-for-investment	$ 36,165,838	$ 35,297,878	$ 32,831,405