Fair Values of Assets and Liabilities (Summary Of Carrying Amounts And Estimated Fair Values Of Financial Instruments) (Detail) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021	Mar. 31, 2021
Financial Assets:
Interest-bearing deposits with banks	$ 4,013,597	$ 5,372,603	$ 3,348,794
Available-for-sale securities	2,998,898	2,327,793	2,430,749
Held-to-maturity securities	3,146,427	2,900,694	2,121,065
Equity securities with readily determinable fair value	92,689	90,511	90,338
FHLB and FRB stock, at cost	136,163	135,378	135,881
Brokerage customer receivables	22,888	26,068	19,056
Mortgage loans held-for-sale, at fair value	606,545	817,912	1,260,193
Accrued interest receivable and other	1,066,750	1,084,115	1,230,362
Financial Liabilities
FHLB advances	1,241,071	1,241,071	1,228,436
Other borrowings	482,516	494,136	516,877
Subordinated notes	437,033	436,938	436,595
Junior subordinated debentures	253,566	253,566	253,566
Carrying Value
Financial Assets:
Cash and cash equivalents	462,572	411,205	426,377
Securities sold under agreements to repurchase with original maturities exceeding three months	700,000	700,000	0
Interest-bearing deposits with banks	4,013,597	5,372,603	3,348,794
Available-for-sale securities	2,998,898	2,327,793	2,430,749
Held-to-maturity securities	3,435,729	2,942,285	2,166,419
Trading account securities	852	1,061	951
Equity securities with readily determinable fair value	92,689	90,511	90,338
FHLB and FRB stock, at cost	136,163	135,378	135,881
Brokerage customer receivables	22,888	26,068	19,056
Mortgage loans held-for-sale, at fair value	606,545	817,912	1,260,193
Nonqualified deferred compensation assets	15,447	16,240	15,891
Derivative assets	153,534	165,008	253,509
Accrued interest receivable and other	278,873	268,921	281,020
Total	48,198,334	48,064,089	43,600,411
Financial Liabilities
Non-maturity deposits	38,483,327	38,126,796	33,061,502
Deposits with stated maturities	3,735,995	3,968,789	4,811,150
FHLB advances	1,241,071	1,241,071	1,228,436
Other borrowings	482,516	494,136	516,877
Subordinated notes	437,033	436,938	436,595
Junior subordinated debentures	253,566	253,566	253,566
Derivative liabilities	122,107	123,000	200,758
Accrued interest payable	14,269	9,304	19,940
Total financial liabilities	44,769,884	44,653,600	40,528,824
Carrying Value | Loans held-for-investment, at fair value
Financial Assets:
Loans held-for-investment	57,984	38,598	51,916
Carrying Value | Loans held-for-investment, at amortized cost
Financial Assets:
Loans held-for-investment	35,222,563	34,750,506	33,119,317
Fair Value
Financial Assets:
Cash and cash equivalents	462,572	411,205	426,377
Securities sold under agreements to repurchase with original maturities exceeding three months	700,000	700,000	0
Interest-bearing deposits with banks	4,013,597	5,372,603	3,348,794
Available-for-sale securities	2,998,898	2,327,793	2,430,749
Held-to-maturity securities	3,146,427	2,900,694	2,121,065
Trading account securities	852	1,061	951
Equity securities with readily determinable fair value	92,689	90,511	90,338
FHLB and FRB stock, at cost	136,163	135,378	135,881
Brokerage customer receivables	22,888	26,068	19,056
Mortgage loans held-for-sale, at fair value	606,545	817,912	1,260,193
Nonqualified deferred compensation assets	15,447	16,240	15,891
Derivative assets	153,534	165,008	253,509
Accrued interest receivable and other	278,873	268,921	281,020
Total	48,676,309	48,569,870	43,502,500
Financial Liabilities
Non-maturity deposits	38,483,327	38,126,796	33,061,502
Deposits with stated maturities	3,735,750	3,965,372	4,801,257
FHLB advances	1,193,080	1,186,280	1,121,269
Other borrowings	483,202	494,670	516,877
Subordinated notes	446,711	472,684	458,832
Junior subordinated debentures	268,913	212,226	208,132
Derivative liabilities	122,107	123,000	200,758
Accrued interest payable	14,269	9,304	19,940
Total financial liabilities	44,747,359	44,590,332	40,388,567
Fair Value | Loans held-for-investment, at fair value
Financial Assets:
Loans held-for-investment	57,984	38,598	51,916
Fair Value | Loans held-for-investment, at amortized cost
Financial Assets:
Loans held-for-investment	$ 35,989,840	$ 35,297,878	$ 33,066,760