Fair Values Of Assets And Liabilities (Summary Of Carrying Amounts And Estimated Fair Values Of Financial Instruments) (Detail) - USD ($) $ in Thousands	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Interest bearing deposits with banks	$ 693,269		$ 607,782	$ 591,721
Available-for-sale securities, at fair value	637,663		1,716,388	2,162,061
Held-to-maturity securities, Amortized Cost	992,211		884,826	0
Trading account securities	3,613		448	1,597
FHLB and FRB stock, at cost	121,319		101,581	89,818
Brokerage customer receivables	26,866		27,631	29,753
Mortgage loans held-for-sale, at fair value	554,256		388,038	497,283
Derivative assets	88,875		42,026	34,851
FDIC indemnification asset	(11,729)	$ (10,029)	(6,100)	3,429	$ 10,224	$ 11,846
Accrued interest receivable and other	670,014		597,099	533,175
FHLB advances	588,055		853,431	435,721
Other borrowings	252,611		265,785	261,674
Subordinated notes	138,915		138,861	138,808
Junior subordinated debentures	253,566		268,566	249,493
Derivative liabilities	90,892		42,458	36,605
Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	271,575		275,795	252,209
Interest bearing deposits with banks	693,269		607,782	591,721
Available-for-sale securities, at fair value	637,663		1,716,388	2,162,061
Held-to-maturity securities, Amortized Cost	992,211		884,826	0
Trading account securities	3,613		448	1,597
FHLB and FRB stock, at cost	121,319		101,581	89,818
Brokerage customer receivables	26,866		27,631	29,753
Mortgage loans held-for-sale, at fair value	554,256		388,038	497,283
Total loans	18,279,903		17,266,790	15,707,060
MSRs	13,382		9,092	8,034
Nonqualified deferred compensation assets	9,076		8,517	8,778
Derivative assets	101,052		51,298	48,918
FDIC indemnification asset	0		0	3,429
Accrued interest receivable and other	198,017		193,092	178,349
Total financial assets	21,902,202		21,531,278	19,579,010
Non-maturity deposits	15,958,500		14,634,957	13,145,542
Deposits with stated maturities	4,083,250		4,004,677	3,936,876
FHLB advances	588,055		853,431	435,721
Other borrowings	252,611		265,785	261,674
Subordinated notes	138,915		138,861	138,808
Junior subordinated debentures	253,566		268,566	249,493
Derivative liabilities	100,912		45,019	40,500
FDIC indemnification liability	11,729		6,100	0
Accrued interest payable	6,175		7,394	6,827
Total financial liabilities	21,393,713		20,224,790	18,215,441
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	271,575		275,795	252,209
Interest bearing deposits with banks	693,269		607,782	591,721
Available-for-sale securities, at fair value	637,663		1,716,388	2,162,061
Held-to-maturity securities, Amortized Cost	1,010,179		878,111	0
Trading account securities	3,613		448	1,597
FHLB and FRB stock, at cost	121,319		101,581	89,818
Brokerage customer receivables	26,866		27,631	29,753
Mortgage loans held-for-sale, at fair value	554,256		388,038	497,283
Total loans	19,228,691		18,106,829	16,469,518
MSRs	13,382		9,092	8,034
Nonqualified deferred compensation assets	9,076		8,517	8,778
Derivative assets	101,052		51,298	48,918
FDIC indemnification asset	0		0	3,429
Accrued interest receivable and other	198,017		193,092	178,349
Total financial assets	22,868,958		22,364,602	20,341,468
Non-maturity deposits	15,958,500		14,634,957	13,145,542
Deposits with stated maturities	4,086,350		3,998,180	3,937,146
FHLB advances	597,568		863,437	448,870
Other borrowings	252,611		265,785	261,674
Subordinated notes	141,858		140,302	142,810
Junior subordinated debentures	254,143		268,046	250,265
Derivative liabilities	100,912		45,019	40,500
FDIC indemnification liability	11,729		6,100	0
Accrued interest payable	6,175		7,394	6,827
Total financial liabilities	$ 21,409,846		$ 20,229,220	$ 18,233,634