Fair Values of Assets and Liabilities (Summary Of Carrying Amounts And Estimated Fair Values Of Financial Instruments) (Detail) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020	Sep. 30, 2020
Financial Assets:
Interest-bearing deposits with banks	$ 5,232,315	$ 4,802,527	$ 3,825,823
Available-for-sale securities	2,373,478	3,055,839	2,946,459
Held-to-maturity securities	2,699,480	593,767	575,947
Equity securities with readily determinable fair value	88,193	90,862	54,398
FHLB and FRB stock, at cost	135,408	135,588	135,568
Brokerage customer receivables	26,378	17,436	16,818
Mortgage loans held-for-sale, at fair value	925,312	1,272,090	959,671
Accrued interest receivable and other	1,166,917	1,351,455	1,424,728
Financial Liabilities
FHLB advances	1,241,071	1,228,429	1,228,422
Other borrowings	504,527	518,928	507,395
Subordinated notes	436,811	436,506	436,385
Junior subordinated debentures	253,566	253,566	253,566
Carrying Value
Financial Assets:
Cash and cash equivalents	462,299	322,474	308,695
Interest-bearing deposits with banks	5,232,315	4,802,527	3,825,823
Available-for-sale securities	2,373,478	3,055,839	2,946,459
Held-to-maturity securities	2,736,722	579,138	560,267
Trading account securities	1,103	671	1,720
Equity securities with readily determinable fair value	88,193	90,862	54,398
FHLB and FRB stock, at cost	135,408	135,588	135,568
Brokerage customer receivables	26,378	17,436	16,818
Mortgage loans held-for-sale, at fair value	925,312	1,272,090	959,671
Nonqualified deferred compensation assets	15,797	15,398	14,197
Derivative assets	191,612	278,423	321,488
Accrued interest receivable and other	272,293	272,339	272,940
Total financial assets	45,724,953	42,921,858	41,553,599
Financial Liabilities
Non-maturity deposits	35,822,012	32,116,023	30,778,127
Deposits with stated maturities	4,130,546	4,976,628	5,066,295
FHLB advances	1,241,071	1,228,429	1,228,422
Other borrowings	504,527	518,928	507,395
Subordinated notes	436,811	436,506	436,385
Junior subordinated debentures	253,566	253,566	253,566
Derivative liabilities	161,314	288,465	326,990
Accrued interest payable	15,030	15,645	21,310
Total financial liabilities	42,564,877	39,834,190	38,618,490
Fair Value
Financial Assets:
Cash and cash equivalents	462,299	322,474	308,695
Interest-bearing deposits with banks	5,232,315	4,802,527	3,825,823
Available-for-sale securities	2,373,478	3,055,839	2,946,459
Held-to-maturity securities	2,699,480	593,767	575,947
Trading account securities	1,103	671	1,720
Equity securities with readily determinable fair value	88,193	90,862	54,398
FHLB and FRB stock, at cost	135,408	135,588	135,568
Brokerage customer receivables	26,378	17,436	16,818
Mortgage loans held-for-sale, at fair value	925,312	1,272,090	959,671
Nonqualified deferred compensation assets	15,797	15,398	14,197
Derivative assets	191,612	278,423	321,488
Accrued interest receivable and other	272,293	272,339	272,940
Total financial assets	45,731,335	42,784,231	41,410,798
Financial Liabilities
Non-maturity deposits	35,822,012	32,116,023	30,778,127
Deposits with stated maturities	4,124,199	4,969,849	5,063,732
FHLB advances	1,164,168	1,172,315	1,207,203
Other borrowings	504,527	518,928	507,395
Subordinated notes	474,171	473,093	473,825
Junior subordinated debentures	207,675	204,713	208,333
Derivative liabilities	161,314	288,465	326,990
Accrued interest payable	15,030	15,645	21,310
Total financial liabilities	42,473,096	39,759,031	38,586,915
Loans held-for-investment, at fair value | Carrying Value
Financial Assets:
Total loans	30,979	55,134	253,515
Loans held-for-investment, at fair value | Fair Value
Financial Assets:
Total loans	30,979	55,134	253,515
Loans held-for-investment, at amortized cost | Carrying Value
Financial Assets:
Total loans	33,233,064	32,023,939	31,882,040
Loans held-for-investment, at amortized cost | Fair Value
Financial Assets:
Total loans	$ 33,276,688	$ 31,871,683	$ 31,723,559