Loans And Allowance For Credit Losses (Summary Of Major Portfolio Segment And Specific Loan Class) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015	Dec. 31, 2014
Financing Receivable, Allowance for Credit Losses [Line Items]
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Provision for Loan Losses	$ (400)	$ (800)
Balance at end of period	611,894	620,013
Loans held for sale	108,764		$ 149,880
Commercial and industrial	13,590,238		13,211,481
Leasing	437,150		441,666
Owner occupied	7,022,429		7,150,028
Municipal	695,436		675,839
Construction and land development	1,967,702		1,841,502
Term	8,826,375		8,514,401
Provision for loan losses	(42,145)	1,494
Change In Allowance Covered By F D I C Indemnification	0	38
Allowance for Loan and Lease Losses, Write-offs	(48,110)	(20,188)
Allowance for Loan and Lease Losses, Recoveries of Bad Debts	11,811	37,070
Net loan and lease charge-offs	(36,299)	16,882
Reserve for unfunded lending commitments	69,026	82,287	74,838	$ 81,076
Provision for Unfunded Lending Commitments	5,812	(1,211)
Total allowance for credit losses	680,920	702,300
Consumer Portfolio Segment [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at end of period	30,195	46,326
Provision for loan losses	5,431	$ (459)
Change In Allowance Covered By F D I C Indemnification	0
Allowance for Loan and Lease Losses, Write-offs	(3,905)	$ (3,611)
Allowance for Loan and Lease Losses, Recoveries of Bad Debts	1,752	2,338
Net loan and lease charge-offs	(2,153)	(1,273)
Reserve for unfunded lending commitments	0	575	616	628
Provision for Unfunded Lending Commitments	616	53
Total allowance for credit losses	30,195	46,901
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at end of period	117,712	131,615
Construction and land development	1,967,702		1,841,502
Term	8,826,375		8,514,401
Provision for loan losses	(1,701)	$ 26,887
Change In Allowance Covered By F D I C Indemnification	0
Allowance for Loan and Lease Losses, Write-offs	(975)	$ (626)
Allowance for Loan and Lease Losses, Recoveries of Bad Debts	2,994	14,119
Net loan and lease charge-offs	2,019	13,493
Reserve for unfunded lending commitments	12,759	18,937	16,526	21,517
Provision for Unfunded Lending Commitments	3,767	2,580
Total allowance for credit losses	130,471	150,552
Commercial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at end of period	463,987	442,072
Commercial and industrial	13,590,238		13,211,481
Leasing	437,150		441,666
Owner occupied	7,022,429		7,150,028
Municipal	695,436		675,839
Provision for loan losses	(45,875)	(24,934)
Change In Allowance Covered By F D I C Indemnification	0	38
Allowance for Loan and Lease Losses, Write-offs	(43,230)	(15,951)
Allowance for Loan and Lease Losses, Recoveries of Bad Debts	7,065	20,613
Net loan and lease charge-offs	(36,165)	4,662
Reserve for unfunded lending commitments	56,267	62,775	$ 57,696	$ 58,931
Provision for Unfunded Lending Commitments	1,429	(3,844)
Total allowance for credit losses	$ 520,254	$ 504,847