Fair Values Of Assets And Liabilities (Summary Of Carrying Amounts And Estimated Fair Values Of Financial Instruments) (Detail) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015	Sep. 30, 2015	Dec. 31, 2014
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	$ 246,947	$ 275,795	$ 250,655	$ 230,707
Interest bearing deposits with banks	816,104	607,782	701,106
Available-for-sale securities	1,650,096	1,716,388	2,214,281
Held-to-maturity securities	942,666	878,111	0
Trading account securities	1,092	448	3,312
FHLB and FRB stock, at cost	129,630	101,581	90,308
Brokerage customer receivables	25,511	27,631	28,293
Mortgage loans held-for-sale, at fair value	559,634	388,038	347,005
Accrued interest receivable and other	660,923	597,099	629,211
FHLB advances	419,632	853,431	443,955
Other borrowings	241,366	265,785	259,805
Subordinated notes	138,943	138,861	138,834
Junior subordinated debentures	253,566	268,566	268,566
Derivative liabilities	87,948	45,019	65,198
Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	246,947	275,795	250,655
Interest bearing deposits with banks	816,104	607,782	701,106
Available-for-sale securities	1,650,096	1,716,388	2,214,281
Held-to-maturity securities	932,767	884,826	0
Trading account securities	1,092	448	3,312
FHLB and FRB stock, at cost	129,630	101,581	90,308
Brokerage customer receivables	25,511	27,631	28,293
Mortgage loans held-for-sale, at fair value	559,634	388,038	347,005
Total loans	19,197,201	17,266,790	16,484,820
MSRs	13,901	9,092	7,875
Nonqualified deferred compensation assets	9,218	8,517	8,342
Derivative assets	88,828	51,298	69,034
Accrued interest receivable and other	205,725	193,092	192,572
Total financial assets	23,876,654	21,531,278	20,397,603
Non-maturity deposits	16,946,178	14,634,957	14,092,697
Deposits with stated maturities	4,201,477	4,004,677	4,135,772
FHLB advances	419,632	853,431	451,330
Other borrowings	241,366	265,785	259,978
Subordinated notes	138,943	138,861	138,834
Junior subordinated debentures	253,566	268,566	268,566
Derivative liabilities	87,948	45,019	65,198
FDIC indemnification liability	17,945	6,100	3,033
Accrued interest payable	8,007	7,394	11,364
Total financial liabilities	22,315,062	20,224,790	19,426,772
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	246,947	275,795	250,655
Interest bearing deposits with banks	816,104	607,782	701,106
Available-for-sale securities	1,650,096	1,716,388	2,214,281
Held-to-maturity securities	942,666	878,111	0
Trading account securities	1,092	448	3,312
FHLB and FRB stock, at cost	129,630	101,581	90,308
Brokerage customer receivables	25,511	27,631	28,293
Mortgage loans held-for-sale, at fair value	559,634	388,038	347,005
Total loans	20,251,518	18,106,829	17,284,375
MSRs	13,901	9,092	7,875
Nonqualified deferred compensation assets	9,218	8,517	8,342
Derivative assets	88,828	51,298	69,034
Accrued interest receivable and other	205,725	193,092	192,572
Total financial assets	24,940,870	22,364,602	21,197,158
Non-maturity deposits	16,946,178	14,634,957	14,092,697
Deposits with stated maturities	4,200,278	3,998,180	4,137,856
FHLB advances	427,103	863,437	459,154
Other borrowings	241,366	265,785	259,978
Subordinated notes	138,715	140,302	142,953
Junior subordinated debentures	254,108	268,046	268,058
Derivative liabilities	87,948	45,019	65,198
FDIC indemnification liability	17,945	6,100	3,033
Accrued interest payable	8,007	7,394	11,364
Total financial liabilities	$ 22,321,648	$ 20,229,220	$ 19,440,291