Fair Values Of Assets And Liabilities (Summary Of Carrying Amounts And Estimated Fair Values Of Financial Instruments) (Detail) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014	Dec. 31, 2013
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Interest bearing deposits with banks		$ 591,721	$ 506,871	$ 591,721	$ 506,871		$ 998,437
Available-for-sale securities, at fair value		2,162,061	1,824,240	2,162,061	1,824,240		1,792,078
Trading account securities		1,597	2,234	1,597	2,234		1,206
Federal Home Loan Bank and Federal Reserve Bank stock, at cost		89,818	84,531	89,818	84,531		91,582
Brokerage customer receivables		29,753	28,199	29,753	28,199		24,221
Mortgage loans held-for-sale, at fair value		497,283	363,627	497,283	363,627		351,290
Derivative assets		34,851	33,723	34,851	33,723		35,070
FDIC indemnification asset		3,429	46,115	3,429	46,115	$ 10,224	11,846	$ 60,298	$ 85,672
Accrued interest receivable and other		556,344	525,394	556,344	525,394		501,882
Federal Home Loan Bank advances		444,017	580,582	444,017	580,582		733,050
Other borrowings		261,908	43,716	261,908	43,716		196,465
Subordinated notes		140,000	140,000	140,000	140,000		140,000
Junior subordinated debentures		249,493	249,493	249,493	249,493		249,493
Derivative liabilities		36,605	36,733	36,605	36,733		36,921
Carrying Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents		252,209	356,978	252,209	356,978		230,707
Interest bearing deposits with banks		591,721	506,871	591,721	506,871		998,437
Available-for-sale securities, at fair value		2,162,061	1,824,240	2,162,061	1,824,240		1,792,078
Trading account securities		1,597	2,234	1,597	2,234		1,206
Federal Home Loan Bank and Federal Reserve Bank stock, at cost		89,818	84,531	89,818	84,531		91,582
Brokerage customer receivables		29,753	28,199	29,753	28,199		24,221
Mortgage loans held-for-sale, at fair value		497,283	363,627	497,283	363,627		351,290
Total loans		15,707,060	14,025,150	15,707,060	14,025,150		14,636,107
Mortgage servicing rights		8,034	8,227	8,034	8,227		8,435
Nonqualified deferred compensation assets		8,778	7,850	8,778	7,850		7,951
Derivative assets		48,918	50,967	48,918	50,967		47,964
FDIC indemnification asset		3,429	46,115	3,429	46,115		11,846
Accrued interest receivable and other		178,349	165,511	178,349	165,511		169,156
Total financial assets		19,579,010	17,470,500	19,579,010	17,470,500		18,370,980
Non-maturity deposits		13,145,542	11,314,162	13,145,542	11,314,162		12,142,034
Deposits with stated maturities		3,936,876	4,242,214	3,936,876	4,242,214		4,139,810
Federal Home Loan Bank advances		444,017	580,582	444,017	580,582		733,050
Other borrowings		261,908	43,716	261,908	43,716		196,465
Subordinated notes		140,000	140,000	140,000	140,000		140,000
Junior subordinated debentures		249,493	249,493	249,493	249,493		249,493
Derivative liabilities		40,500	43,650	40,500	43,650		41,180
Accrued interest payable		6,827	8,399	6,827	8,399		8,001
Total financial liabilities		18,225,163	16,622,216	18,225,163	16,622,216		17,650,033
Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents		252,209	356,978	252,209	356,978		230,707
Interest bearing deposits with banks		591,721	506,871	591,721	506,871		998,437
Available-for-sale securities, at fair value		2,162,061	1,824,240	2,162,061	1,824,240		1,792,078
Trading account securities		1,597	2,234	1,597	2,234		1,206
Federal Home Loan Bank and Federal Reserve Bank stock, at cost		89,818	84,531	89,818	84,531		91,582
Brokerage customer receivables		29,753	28,199	29,753	28,199		24,221
Mortgage loans held-for-sale, at fair value		497,283	363,627	497,283	363,627		351,290
Total loans		16,469,518	14,741,579	16,469,518	14,741,579		15,346,266
Mortgage servicing rights		8,034	8,227	8,034	8,227		8,435
Nonqualified deferred compensation assets		8,778	7,850	8,778	7,850		7,951
Derivative assets		48,918	50,967	48,918	50,967		47,964
FDIC indemnification asset		3,429	46,115	3,429	46,115		11,846
Accrued interest receivable and other		178,349	165,511	178,349	165,511		169,156
Total financial assets		20,341,468	18,186,929	20,341,468	18,186,929		19,081,139
Non-maturity deposits		13,145,542	11,314,162	13,145,542	11,314,162		12,142,034
Deposits with stated maturities		3,937,146	4,255,896	3,937,146	4,255,896		4,143,161
Federal Home Loan Bank advances		448,870	585,792	448,870	585,792		738,113
Other borrowings		261,908	43,716	261,908	43,716		197,883
Subordinated notes		142,810	144,899	142,810	144,899		143,639
Junior subordinated debentures		250,265	250,492	250,265	250,492		250,305
Derivative liabilities		40,500	43,650	40,500	43,650		41,180
Accrued interest payable		6,827	8,399	6,827	8,399		8,001
Total financial liabilities		18,233,868	16,647,006	18,233,868	16,647,006		17,664,316
Municipal
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value		58,572	38,053	58,572	38,053	56,049	58,953	39,772	36,386
Available-for-sale securities, at fair value		269,790	176,107	269,790	176,107		238,529
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Other Comprehensive Income (Loss)		(713)	73	(510)	220
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases		4,175	1,606	10,849	4,966
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements		(939)	(3,398)	(10,720)	(3,519)
Equity securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value		24,996	24,152	24,996	24,152	24,656	23,711	23,438	22,163
Available-for-sale securities, at fair value		54,208	54,852	54,208	54,852		51,139
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Other Comprehensive Income (Loss)		340	714	1,285	1,989
Mortgage Servicing Rights
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value		8,034	8,227	8,034	8,227	$ 7,852	$ 8,435	$ 8,719	$ 8,946
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings	[1]	$ 182	$ (492)	$ (401)	$ (719)

[1] Changes in the balance of mortgage servicing rights are recorded as a component of mortgage banking revenue in non-interest income.