Fair Values Of Assets And Liabilities (Summary Of Carrying Amounts And Estimated Fair Values Of Financial Instruments) (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016	Jun. 30, 2016	Dec. 31, 2015
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	$ 296,161	$ 270,045	$ 271,575	$ 275,795
Interest bearing deposits with banks	1,011,635	980,457	693,269
Available-for-sale securities	1,649,636	1,724,667	637,663
Held-to-maturity securities	787,489	607,602	1,010,179
Trading account securities	1,987	1,989	3,613
FHLB and FRB stock, at cost	80,812	133,494	121,319
Brokerage customer receivables	23,281	25,181	26,866
Mortgage loans held-for-sale, at fair value	382,837	418,374	554,256
Accrued interest receivable and other	577,359	593,796	670,014
FHLB advances	318,270	153,831	588,055
Other borrowings	277,710	262,486	252,611
Subordinated notes	139,029	138,971	138,915
Junior subordinated debentures	253,566	253,566	253,566
Derivative liabilities	37,651	39,839	100,912
Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	296,161	270,045	271,575
Interest bearing deposits with banks	1,011,635	980,457	693,269
Available-for-sale securities	1,649,636	1,724,667	637,663
Held-to-maturity securities	793,376	635,705	992,211
Trading account securities	1,987	1,989	3,613
FHLB and FRB stock, at cost	80,812	133,494	121,319
Brokerage customer receivables	23,281	25,181	26,866
Mortgage loans held-for-sale, at fair value	382,837	418,374	554,256
Loans held-for-investment, at fair value	30,173	22,137	16,294
Loans held-for-investment, at amortized cost	20,763,278	19,739,180	18,263,609
MSRs	27,307	19,103	13,382
Nonqualified deferred compensation assets	10,556	9,228	9,076
Derivative assets	49,703	56,394	101,052
Accrued interest receivable and other	215,291	204,513	198,017
Total financial assets	25,336,033	24,240,467	21,902,202
Non-maturity deposits	18,086,300	17,383,729	15,958,500
Deposits with stated maturities	4,519,392	4,274,903	4,083,250
FHLB advances	318,270	153,831	588,055
Other borrowings	277,710	262,486	252,611
Subordinated notes	139,029	138,971	138,915
Junior subordinated debentures	253,566	253,566	253,566
Derivative liabilities	37,651	39,839	100,912
FDIC indemnification liability	15,375	16,701	11,729
Accrued interest payable	6,460	6,421	6,175
Total financial liabilities	23,653,753	22,530,447	21,393,713
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	296,161	270,045	271,575
Interest bearing deposits with banks	1,011,635	980,457	693,269
Available-for-sale securities	1,649,636	1,724,667	637,663
Held-to-maturity securities	787,489	607,602	1,010,179
Trading account securities	1,987	1,989	3,613
FHLB and FRB stock, at cost	80,812	133,494	121,319
Brokerage customer receivables	23,281	25,181	26,866
Mortgage loans held-for-sale, at fair value	382,837	418,374	554,256
Loans held-for-investment, at fair value	30,173	22,137	16,294
Loans held-for-investment, at amortized cost	21,921,002	20,755,320	19,212,397
MSRs	27,307	19,103	13,382
Nonqualified deferred compensation assets	10,556	9,228	9,076
Derivative assets	49,703	56,394	101,052
Accrued interest receivable and other	215,291	204,513	198,017
Total financial assets	26,487,870	25,228,504	22,868,958
Non-maturity deposits	18,086,300	17,383,729	15,958,500
Deposits with stated maturities	4,503,645	4,263,576	4,086,350
FHLB advances	316,799	157,051	597,568
Other borrowings	277,710	262,486	252,611
Subordinated notes	143,126	135,268	141,858
Junior subordinated debentures	253,330	254,384	254,143
Derivative liabilities	37,651	39,839	100,912
FDIC indemnification liability	15,375	16,701	11,729
Accrued interest payable	6,460	6,421	6,175
Total financial liabilities	$ 23,640,396	$ 22,519,455	$ 21,409,846