Fair Value Measurement (Fair Value Disclosure by Balance Sheet Grouping ) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2014
Financial assets:
Cash and Cash Equivalents, at Carrying Value	$ 524,287	$ 587,589	$ 524,287	$ 587,589	$ 463,817			$ 697,424
Cash and due from banks, Fair Value	524,287	587,589	524,287	587,589	463,817
Available-for-sale Securities, Carrying Amount	4,318,688	3,838,509	4,318,688	3,838,509	3,967,735
Held-to-maturity Securities, Carrying Amount	2,514,161	2,787,513	2,514,161	2,787,513	2,674,093
Held-to-maturity Securities, Fair Value	2,545,740	2,760,120	2,545,740	2,760,120	2,659,119
Other Investments, Carrying Amount	148,367	147,967	148,367	147,967	148,172
Other Investments, Fair Value	148,367	147,967	148,367	147,967	148,172
Loans held for sale	3,962	5,432	3,962	5,432	5,472
Loans and Leases Receivable, Net Amount	16,193,957	15,556,851	16,193,957	15,556,851	15,923,254
Net covered loans and loss share receivable, Fair Value	149,121	211,887	149,121	211,887	170,690
Accrued interest receivable, Carrying Amount	65,666	66,501	65,666	66,501	67,887
Accrued interest receivable, Fair Value	65,666	66,501	65,666	66,501	67,887
Derivative Assets, Carrying Amount	117,842	48,073	117,842	48,073	58,107
Derivative Asset, Fair Value, Gross Asset	117,842	48,073	117,842	48,073	58,107
Financial liabilities:
Deposits, Carrying Amount	20,952,643	19,673,850	20,952,643	19,673,850	20,108,003
Deposits, Fair Value	20,960,182	19,681,270	20,960,182	19,681,270	20,116,298
Total Federal funds purchased and securities sold under agreements to repurchase, Carrying Amount	686,890	1,519,250	686,890	1,519,250	1,037,075
Federal funds purchased and securities sold under agreements to repurchase, Fair Value	686,890	1,519,250	686,890	1,519,250	1,037,075
Wholesale Borrowings, Carrying Amount	468,447	366,074	468,447	366,074	580,648
Other Borrowings, Fair Value	473,187	369,337	473,187	369,337	582,120
Long-term Debt	526,389	497,393	526,389	497,393	505,173
Long-term Debt, Fair Value	522,151	509,900	522,151	509,900	503,675
Accrued interest payable, Carrying Amount	10,632	9,910	10,632	9,910	10,758
Accrued interest payable, Fair Value	10,632	9,910	10,632	9,910	10,758
Derivative liabilities, Carrying Amount	90,622	51,497	90,622	51,497	52,745
Derivative Liability, Fair Value, Gross Liability	90,622	51,497	90,622	51,497	52,745
Mortgage Servicing rights Valuation Allowance	(1,549)	(490)	(1,549)	(490)	(399)	$ (868)	$ (1,131)	$ (955)
Mortgage Servicing Rights Net Carrying balance	15,761	20,145	15,761	20,145	18,500
Mortgage Servicing Rights (MSR) Impairment (Recovery)	681	(641)	1,150	(465)	(600)
Impaired Collateral Dependant Loans, Recorded Investment	116,100	82,700	116,100	82,700	84,300
Determination Of Specific Allowance For Loan Losses	11,900	10,200	11,900	10,200	12,900
Fair Value, Inputs, Level 1
Financial assets:
Cash and due from banks, Fair Value		587,589		587,589	463,817
Available-for-sale Securities, Carrying Amount	2,788	2,824	2,788	2,824	2,821
Held-to-maturity Securities, Fair Value	0	0	0	0	0
Other Investments, Fair Value	0	0	0	0	0
Loans held for sale	0	0	0	0	0
Net covered loans and loss share receivable, Fair Value	0	0	0	0	0
Accrued interest receivable, Fair Value	0	0	0	0	0
Derivative Asset, Fair Value, Gross Asset	0	0	0	0	0
Financial liabilities:
Deposits, Fair Value	0	0	0	0	0
Federal funds purchased and securities sold under agreements to repurchase, Fair Value	0	0	0	0	0
Other Borrowings, Fair Value	0	0	0	0	0
Long-term Debt, Fair Value	0	0	0	0	0
Accrued interest payable, Fair Value	0	0	0	0	0
Derivative Liability, Fair Value, Gross Liability	0	0	0	0	0
Fair Value, Inputs, Level 2
Financial assets:
Cash and due from banks, Fair Value	0	0	0	0	0
Available-for-sale Securities, Carrying Amount	3,972,996	3,524,149	3,972,996	3,524,149	3,623,270
Held-to-maturity Securities, Fair Value		2,760,120		2,760,120	2,659,119
Other Investments, Fair Value		147,967		147,967	148,172
Loans held for sale	3,962	5,432	3,962	5,432	5,472
Net covered loans and loss share receivable, Fair Value	0	0	0	0	0
Accrued interest receivable, Fair Value	65,666	66,501	65,666	66,501	67,887
Derivative Asset, Fair Value, Gross Asset	117,842	48,073	117,842	48,073	58,107
Financial liabilities:
Deposits, Fair Value	20,960,182	19,681,270	20,960,182	19,681,270	20,116,298
Federal funds purchased and securities sold under agreements to repurchase, Fair Value		1,519,250		1,519,250	1,037,075
Other Borrowings, Fair Value	473,187	369,337	473,187	369,337	582,120
Long-term Debt, Fair Value	522,151	509,900	522,151	509,900	503,675
Accrued interest payable, Fair Value	10,632	9,910	10,632	9,910	10,758
Derivative Liability, Fair Value, Gross Liability	90,622	51,497	90,622	51,497	52,745
Level 3
Financial assets:
Cash and due from banks, Fair Value	0	0	0	0	0
Available-for-sale Securities, Carrying Amount	342,904	311,536	342,904	311,536	341,644
Held-to-maturity Securities, Fair Value	0	0	0	0	0
Other Investments, Fair Value	0	0	0	0	0
Loans held for sale	0	0	0	0	0
Net covered loans and loss share receivable, Fair Value		211,887		211,887
Accrued interest receivable, Fair Value	0	0	0	0	0
Derivative Asset, Fair Value, Gross Asset	0	0	0	0	0
Financial liabilities:
Deposits, Fair Value	0	0	0	0	0
Federal funds purchased and securities sold under agreements to repurchase, Fair Value	0	0	0	0	0
Other Borrowings, Fair Value	0	0	0	0	0
Long-term Debt, Fair Value	0	0	0	0	0
Accrued interest payable, Fair Value	0	0	0	0	0
Derivative Liability, Fair Value, Gross Liability	0	0	0	0	0
Originated Loans
Financial assets:
Loans and Leases Receivable, Net Amount	14,560,456	13,254,230	14,560,456	13,254,230	14,013,370
Originated Loans and Leases Receivable Fair Value	14,349,013	13,077,485	14,349,013	13,077,485	13,795,058
Originated Loans | Fair Value, Inputs, Level 1
Financial assets:
Loans and Leases Receivable, Net Amount	0	0	0	0	0
Originated Loans | Fair Value, Inputs, Level 2
Financial assets:
Loans and Leases Receivable, Net Amount	0	0	0	0	0
Originated Loans | Level 3
Financial assets:
Loans and Leases Receivable, Net Amount	14,349,013	13,077,485	14,349,013	13,077,485	13,795,058
Acquired Loans
Financial assets:
Loans and Leases Receivable, Net Amount	1,484,380	2,090,734	1,484,380	2,090,734	1,739,194
Originated Loans and Leases Receivable Fair Value	1,532,344	2,167,304	1,532,344	2,167,304	1,796,314
Acquired Loans | Fair Value, Inputs, Level 1
Financial assets:
Loans and Leases Receivable, Net Amount	0	0	0	0	0
Acquired Loans | Fair Value, Inputs, Level 2
Financial assets:
Loans and Leases Receivable, Net Amount	0	0	0	0	0
Acquired Loans | Level 3
Financial assets:
Loans and Leases Receivable, Net Amount	$ 1,532,344	$ 2,167,304	$ 1,532,344	$ 2,167,304	$ 1,796,314