Loans And Allowance For Credit Losses (Narrative) (Details)		3 Months Ended		12 Months Ended
		Mar. 31, 2016 USD ($) mo Billing_Cycles d Payments	Mar. 31, 2015 USD ($)	Mar. 31, 2016 USD ($)	Mar. 31, 2015 USD ($)	Dec. 31, 2015 USD ($)
Loans And Allowance For Credit Losses [Line Items]
Unfunded Lending Commitments on Troubled Debt Restructuring		$ 1,600,000		$ 1,600,000		$ 7,500,000
Loans and Leases Receivable, Gross		41,418,185,000		41,418,185,000		40,649,542,000
Financing Receivable, Recorded Investment, Current		41,131,196,000		41,131,196,000		40,363,353,000
Threshold for Internal risk grades assigned to commercial and commercial real estate loans		750,000		750,000
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Provision for Loan Losses		(400,000)	$ (800,000)
Financing Receivable, Modifications, Subsequent Default, Recorded Investment		6,746,000	2,424,000	180,300,000	$ 74,500,000
Unearned income and fees, net of related costs		148,500,000		148,500,000		150,300,000
Owner occupied and commercial real estate loans, unamortized premiums		24,900,000		24,900,000		26,200,000
Land Development Loans		286,800,000		286,800,000		288,000,000
Loans at carrying value pledged as collateral for current and potential borrowings		25,300,000,000		25,300,000,000		19,400,000,000
Payments for Origination and Purchases of Loans Held-for-sale		235,700,000	309,700,000
Loans and Leases Receivable, Gain (Loss) on Sales, Net		3,000,000	4,600,000
Principle amount of loans held for sale sold		273,200,000	300,400,000
Servicing Asset at Amortized Cost		$ 0		0		0
Number of days for consumer loans to be charged off | d		180
Number of days for closed-end loans to be charged off | d		120
Minimum number of days past due for nonaccrual status | d		90
Minimum number of monthly payments in arrears when reporting past due | Payments		2
Minimum number of billing cycles in arrears when reported as past due | Billing_Cycles		2
Minimum number of days unpaid when reported as past due | d		30
Threshold for nonaccrual loans for evaluation of impairment		$ 1,000,000
Minimum number of months for borrower to meet terms For TDR status | mo		6
Recorded investment in TDR loans modified with interest rates below market		$ 174,500,000		174,500,000		188,000,000
Total reversal amount to ALLL		400,000	1,400,000
Additional interest income due to increased cash flows from acquired loans		4,500,000	7,400,000
Provision for Loan and Lease Losses		42,145,000	(1,494,000)
Provision for Unfunded Lending Commitments		5,812,000	(1,211,000)
Other Real Estate, Foreclosed Assets, and Repossessed Assets		3,400,000		3,400,000		500,000
Other Real Estate, In Process of Forecloseing Assets		11,300,000		11,300,000		12,500,000
Financing Receivable Recorded Investment Thirty To Eighty Nine Days Past Due		149,270,000		149,270,000		147,980,000
Financing Receivable Recorded Investments, Equal To and Greater Than 90 Days Past Due		137,719,000		137,719,000		138,209,000
Financing Receivable, Recorded Investment, Past Due		286,989,000		286,989,000		286,189,000
Financing Receivable, Recorded Investment, 90 Days Past Due and Still Accruing		37,202,000		37,202,000		32,024,000
Financing Receivable, Recorded Investment, Nonaccrual Status	[1]	392,322,000		392,322,000		217,427,000
Commercial [Member]
Loans And Allowance For Credit Losses [Line Items]
Loans and Leases Receivable, Gross		$ 21,745,253,000		21,745,253,000		21,479,014,000
Subsequent payment default period, number of days | d		90
Provision for Loan and Lease Losses		$ 45,875,000	24,934,000
Provision for Unfunded Lending Commitments		1,429,000	(3,844,000)
Consumer Portfolio Segment [Member]
Loans And Allowance For Credit Losses [Line Items]
Loans and Leases Receivable, Gross		$ 8,878,855,000		8,878,855,000		8,814,625,000
Subsequent payment default period, number of days | d		60
Provision for Loan and Lease Losses		$ (5,431,000)	459,000
Provision for Unfunded Lending Commitments		616,000	53,000
Financing Receivable, Recorded Investment, Nonaccrual Status		202,000		202,000		186,000
Consumer Loan [Member]
Loans And Allowance For Credit Losses [Line Items]
Loans and Leases Receivable, Gross		8,878,855,000		8,878,855,000		8,814,625,000
Financing Receivable, Recorded Investment, Current		8,827,112,000		8,827,112,000		8,750,302,000
Financing Receivable Recorded Investment Thirty To Eighty Nine Days Past Due		23,868,000		23,868,000		30,646,000
Financing Receivable Recorded Investments, Equal To and Greater Than 90 Days Past Due		27,875,000		27,875,000		33,677,000
Financing Receivable, Recorded Investment, Past Due		51,743,000		51,743,000		64,323,000
Financing Receivable, Recorded Investment, 90 Days Past Due and Still Accruing		1,169,000		1,169,000		3,590,000
Financing Receivable, Recorded Investment, Nonaccrual Status	[1]	26,508,000		26,508,000		24,629,000
Consumer Portfolio Segment [Member]
Loans And Allowance For Credit Losses [Line Items]
Loans and Leases Receivable, Gross		188,451,000		188,451,000		187,149,000
Financing Receivable, Recorded Investment, Current		187,760,000		187,760,000		186,436,000
Financing Receivable Recorded Investment Thirty To Eighty Nine Days Past Due		630,000		630,000		647,000
Financing Receivable Recorded Investments, Equal To and Greater Than 90 Days Past Due		61,000		61,000		66,000
Financing Receivable, Recorded Investment, Past Due		691,000		691,000		713,000
Financing Receivable, Recorded Investment, 90 Days Past Due and Still Accruing		0		0		0
Financing Receivable, Recorded Investment, Nonaccrual Status	[1]	78,000		78,000		83,000
Commercial and Industrial Sector [Member]
Loans And Allowance For Credit Losses [Line Items]
Loans and Leases Receivable, Gross		13,590,238,000		13,590,238,000		13,211,481,000
Financing Receivable, Recorded Investment, Current		13,464,106,000		13,464,106,000		13,114,045,000
Financing Receivable Recorded Investment Thirty To Eighty Nine Days Past Due		90,610,000		90,610,000		60,523,000
Financing Receivable Recorded Investments, Equal To and Greater Than 90 Days Past Due		35,522,000		35,522,000		36,913,000
Financing Receivable, Recorded Investment, Past Due		126,132,000		126,132,000		97,436,000
Financing Receivable, Recorded Investment, 90 Days Past Due and Still Accruing		4,388,000		4,388,000		3,065,000
Financing Receivable, Recorded Investment, Nonaccrual Status	[1]	287,662,000		287,662,000		117,942,000
Finance Leases Portfolio Segment [Member]
Loans And Allowance For Credit Losses [Line Items]
Loans and Leases Receivable, Gross		437,150,000		437,150,000		441,666,000
Financing Receivable, Recorded Investment, Current		436,597,000		436,597,000		440,963,000
Financing Receivable Recorded Investment Thirty To Eighty Nine Days Past Due		59,000		59,000		183,000
Financing Receivable Recorded Investments, Equal To and Greater Than 90 Days Past Due		494,000		494,000		520,000
Financing Receivable, Recorded Investment, Past Due		553,000		553,000		703,000
Financing Receivable, Recorded Investment, 90 Days Past Due and Still Accruing		0		0		0
Financing Receivable, Recorded Investment, Nonaccrual Status	[1]	13,613,000		13,613,000		3,309,000
Owner Occupied [Member]
Loans And Allowance For Credit Losses [Line Items]
Loans and Leases Receivable, Gross		7,022,429,000		7,022,429,000		7,150,028,000
Financing Receivable, Recorded Investment, Current		6,965,082,000		6,965,082,000		7,085,086,000
Financing Receivable Recorded Investment Thirty To Eighty Nine Days Past Due		21,987,000		21,987,000		37,776,000
Financing Receivable Recorded Investments, Equal To and Greater Than 90 Days Past Due		35,360,000		35,360,000		27,166,000
Financing Receivable, Recorded Investment, Past Due		57,347,000		57,347,000		64,942,000
Financing Receivable, Recorded Investment, 90 Days Past Due and Still Accruing		13,350,000		13,350,000		3,626,000
Financing Receivable, Recorded Investment, Nonaccrual Status	[1]	46,289,000		46,289,000		43,984,000
Municipal [Member]
Loans And Allowance For Credit Losses [Line Items]
Loans and Leases Receivable, Gross		695,436,000		695,436,000		675,839,000
Financing Receivable, Recorded Investment, Current		695,436,000		695,436,000		668,207,000
Financing Receivable Recorded Investment Thirty To Eighty Nine Days Past Due		0		0		7,586,000
Financing Receivable Recorded Investments, Equal To and Greater Than 90 Days Past Due		0		0		46,000
Financing Receivable, Recorded Investment, Past Due		0		0		7,632,000
Financing Receivable, Recorded Investment, 90 Days Past Due and Still Accruing		0		0		46,000
Financing Receivable, Recorded Investment, Nonaccrual Status	[1]	926,000		926,000		951,000
Commercial Loan [Member]
Loans And Allowance For Credit Losses [Line Items]
Loans and Leases Receivable, Gross		21,745,253,000		21,745,253,000		21,479,014,000
Financing Receivable, Recorded Investment, Current		21,561,221,000		21,561,221,000		21,308,301,000
Financing Receivable Recorded Investment Thirty To Eighty Nine Days Past Due		112,656,000		112,656,000		106,068,000
Financing Receivable Recorded Investments, Equal To and Greater Than 90 Days Past Due		71,376,000		71,376,000		64,645,000
Financing Receivable, Recorded Investment, Past Due		184,032,000		184,032,000		170,713,000
Financing Receivable, Recorded Investment, 90 Days Past Due and Still Accruing		17,738,000		17,738,000		6,737,000
Financing Receivable, Recorded Investment, Nonaccrual Status	[1]	348,490,000		348,490,000		166,186,000
Commercial Real Estate [Member]
Loans And Allowance For Credit Losses [Line Items]
Loans and Leases Receivable, Gross		1,967,702,000		1,967,702,000		1,841,502,000
Financing Receivable, Recorded Investment, Current		1,960,562,000		1,960,562,000		1,835,360,000
Financing Receivable Recorded Investment Thirty To Eighty Nine Days Past Due		2,573,000		2,573,000		842,000
Financing Receivable Recorded Investments, Equal To and Greater Than 90 Days Past Due		4,567,000		4,567,000		5,300,000
Financing Receivable, Recorded Investment, Past Due		7,140,000		7,140,000		6,142,000
Financing Receivable, Recorded Investment, 90 Days Past Due and Still Accruing		0		0		0
Financing Receivable, Recorded Investment, Nonaccrual Status	[1]	1,533,000		1,533,000		1,745,000
Term [Member]
Loans And Allowance For Credit Losses [Line Items]
Loans and Leases Receivable, Gross		8,826,375,000		8,826,375,000		8,514,401,000
Financing Receivable, Recorded Investment, Current		8,782,301,000		8,782,301,000		8,469,390,000
Financing Receivable Recorded Investment Thirty To Eighty Nine Days Past Due		10,173,000		10,173,000		10,424,000
Financing Receivable Recorded Investments, Equal To and Greater Than 90 Days Past Due		33,901,000		33,901,000		34,587,000
Financing Receivable, Recorded Investment, Past Due		44,074,000		44,074,000		45,011,000
Financing Receivable, Recorded Investment, 90 Days Past Due and Still Accruing		18,295,000		18,295,000		21,697,000
Financing Receivable, Recorded Investment, Nonaccrual Status	[1]	15,791,000		15,791,000		24,867,000
Commercial Real Estate [Member]
Loans And Allowance For Credit Losses [Line Items]
Loans and Leases Receivable, Gross		10,794,077,000		10,794,077,000		10,355,903,000
Financing Receivable, Recorded Investment, Current		10,742,863,000		10,742,863,000		10,304,750,000
Financing Receivable Recorded Investment Thirty To Eighty Nine Days Past Due		12,746,000		12,746,000		11,266,000
Financing Receivable Recorded Investments, Equal To and Greater Than 90 Days Past Due		38,468,000		38,468,000		39,887,000
Financing Receivable, Recorded Investment, Past Due		51,214,000		51,214,000		51,153,000
Financing Receivable, Recorded Investment, 90 Days Past Due and Still Accruing		18,295,000		18,295,000		21,697,000
Financing Receivable, Recorded Investment, Nonaccrual Status	[1]	17,324,000		17,324,000		26,612,000
Home Equity Line of Credit [Member]
Loans And Allowance For Credit Losses [Line Items]
Loans and Leases Receivable, Gross		2,432,632,000		2,432,632,000		2,416,357,000
Financing Receivable, Recorded Investment, Current		2,420,364,000		2,420,364,000		2,407,972,000
Financing Receivable Recorded Investment Thirty To Eighty Nine Days Past Due		7,015,000		7,015,000		4,717,000
Financing Receivable Recorded Investments, Equal To and Greater Than 90 Days Past Due		5,253,000		5,253,000		3,668,000
Financing Receivable, Recorded Investment, Past Due		12,268,000		12,268,000		8,385,000
Financing Receivable, Recorded Investment, 90 Days Past Due and Still Accruing		0		0		0
Financing Receivable, Recorded Investment, Nonaccrual Status	[1]	4,604,000		4,604,000		3,053,000
One Through Four Family Residential [Member]
Loans And Allowance For Credit Losses [Line Items]
Loans and Leases Receivable, Gross		5,417,810,000		5,417,810,000		5,382,099,000
Financing Receivable, Recorded Investment, Current		5,386,087,000		5,386,087,000		5,340,549,000
Financing Receivable Recorded Investment Thirty To Eighty Nine Days Past Due		10,617,000		10,617,000		14,828,000
Financing Receivable Recorded Investments, Equal To and Greater Than 90 Days Past Due		21,106,000		21,106,000		26,722,000
Financing Receivable, Recorded Investment, Past Due		31,723,000		31,723,000		41,550,000
Financing Receivable, Recorded Investment, 90 Days Past Due and Still Accruing		321,000		321,000		1,036,000
Financing Receivable, Recorded Investment, Nonaccrual Status	[1]	20,131,000		20,131,000		20,939,000
Construction And Other Consumer Real Estate [Member]
Loans And Allowance For Credit Losses [Line Items]
Loans and Leases Receivable, Gross		401,422,000		401,422,000		385,240,000
Financing Receivable, Recorded Investment, Current		397,809,000		397,809,000		374,987,000
Financing Receivable Recorded Investment Thirty To Eighty Nine Days Past Due		3,365,000		3,365,000		8,593,000
Financing Receivable Recorded Investments, Equal To and Greater Than 90 Days Past Due		248,000		248,000		1,660,000
Financing Receivable, Recorded Investment, Past Due		3,613,000		3,613,000		10,253,000
Financing Receivable, Recorded Investment, 90 Days Past Due and Still Accruing		0		0		1,337,000
Financing Receivable, Recorded Investment, Nonaccrual Status	[1]	355,000		355,000		408,000
Revolving Credit Facility [Member]
Loans And Allowance For Credit Losses [Line Items]
Loans and Leases Receivable, Gross		438,540,000		438,540,000		443,780,000
Financing Receivable, Recorded Investment, Current		435,092,000		435,092,000		440,358,000
Financing Receivable Recorded Investment Thirty To Eighty Nine Days Past Due		2,241,000		2,241,000		1,861,000
Financing Receivable Recorded Investments, Equal To and Greater Than 90 Days Past Due		1,207,000		1,207,000		1,561,000
Financing Receivable, Recorded Investment, Past Due		3,448,000		3,448,000		3,422,000
Financing Receivable, Recorded Investment, 90 Days Past Due and Still Accruing		848,000		848,000		1,217,000
Financing Receivable, Recorded Investment, Nonaccrual Status	[1]	1,340,000		1,340,000		146,000
Accruing [Member]
Loans And Allowance For Credit Losses [Line Items]
Financing Receivable, Modifications, Recorded Investment		195,482,000		195,482,000		194,084,000
Financing Receivable, Modifications, Subsequent Default, Recorded Investment		3,350,000	110,000
Nonaccruing [Member]
Loans And Allowance For Credit Losses [Line Items]
Financing Receivable, Modifications, Recorded Investment		328,006,000		328,006,000		297,088,000
Financing Receivable, Modifications, Subsequent Default, Recorded Investment		3,396,000	$ 2,314,000
Nonaccruing [Member] | Consumer Portfolio Segment [Member]
Loans And Allowance For Credit Losses [Line Items]
Financing Receivable, Modifications, Recorded Investment		$ 12,483,000		$ 12,483,000		$ 13,346,000

[1] 1 Represents nonaccrual loans that are not past due more than 30 days; however, full payment of principal and interest is still not expected.