Fair Values Of Assets And Liabilities (Summary Of Carrying Amounts And Estimated Fair Values Of Financial Instruments) (Detail) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2015	Dec. 31, 2014
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Interest bearing deposits with banks	$ 817,013	$ 607,782	$ 697,799
Available-for-sale securities, at fair value	770,983	1,716,388	1,721,030
Held-to-maturity securities, Amortized Cost	911,715	884,826	0
Trading account securities	2,116	448	7,811
Federal Home Loan Bank and Federal Reserve Bank stock, at cost	113,222	101,581	92,948
Brokerage customer receivables	28,266	27,631	25,287
Mortgage loans held-for-sale, at fair value	314,554	388,038	446,355
Derivative assets	73,829	42,026	45,987
FDIC indemnification asset	0	0	10,224	$ 11,846
Accrued interest receivable and other	647,853	597,099	526,029
Federal Home Loan Bank advances	799,482	853,431	406,839
Other borrowings	253,126	265,785	186,716
Subordinated notes	138,888	138,861	138,782
Junior subordinated debentures	253,566	268,566	249,493
Derivative liabilities	74,019	42,458	47,698
FDIC Indemnification Liability	10,029	6,100
Carrying Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	212,300	275,795	290,872
Interest bearing deposits with banks	817,013	607,782	697,799
Available-for-sale securities, at fair value	770,983	1,716,388	1,721,030
Held-to-maturity securities, Amortized Cost	911,715	884,826	0
Trading account securities	2,116	448	7,811
Federal Home Loan Bank and Federal Reserve Bank stock, at cost	113,222	101,581	92,948
Brokerage customer receivables	28,266	27,631	25,287
Mortgage loans held-for-sale, at fair value	314,554	388,038	446,355
Total loans	17,585,261	17,266,790	15,162,753
Mortgage servicing rights	10,128	9,092	7,852
Nonqualified deferred compensation assets	8,926	8,517	8,718
Derivative assets	86,337	51,298	62,984
FDIC indemnification asset	0	0	10,224
Accrued interest receivable and other	202,018	193,092	181,998
Total financial assets	21,062,839	21,531,278	18,716,631
Non-maturity deposits	15,260,229	14,634,957	12,927,014
Deposits with stated maturities	3,956,842	4,004,677	4,011,755
Federal Home Loan Bank advances	799,482	853,431	406,839
Other borrowings	253,126	265,785	186,716
Subordinated notes	138,888	138,861	138,782
Junior subordinated debentures	253,566	268,566	249,493
Derivative liabilities	81,712	45,019	55,225
FDIC Indemnification Liability	10,029	6,100	0
Accrued interest payable	9,208	7,394	8,583
Total financial liabilities	20,763,082	20,224,790	17,984,407
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	212,300	275,795	290,872
Interest bearing deposits with banks	817,013	607,782	697,799
Available-for-sale securities, at fair value	770,983	1,716,388	1,721,030
Held-to-maturity securities, Amortized Cost	924,344	878,111	0
Trading account securities	2,116	448	7,811
Federal Home Loan Bank and Federal Reserve Bank stock, at cost	113,222	101,581	92,948
Brokerage customer receivables	28,266	27,631	25,287
Mortgage loans held-for-sale, at fair value	314,554	388,038	446,355
Total loans	18,551,606	18,106,829	15,868,532
Mortgage servicing rights	10,128	9,092	7,852
Nonqualified deferred compensation assets	8,926	8,517	8,718
Derivative assets	86,337	51,298	62,984
FDIC indemnification asset	0	0	10,224
Accrued interest receivable and other	202,018	193,092	181,998
Total financial assets	22,041,813	22,364,602	19,422,410
Non-maturity deposits	15,260,229	14,634,957	12,927,014
Deposits with stated maturities	3,956,157	3,998,180	4,017,565
Federal Home Loan Bank advances	807,265	863,437	422,305
Other borrowings	253,126	265,785	186,716
Subordinated notes	139,849	140,302	147,851
Junior subordinated debentures	254,290	268,046	250,196
Derivative liabilities	81,712	45,019	55,225
FDIC Indemnification Liability	10,029	6,100	0
Accrued interest payable	9,208	7,394	8,583
Total financial liabilities	$ 20,771,865	$ 20,229,220	$ 18,015,455