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, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2013
Financial assets:
Cash and Cash Equivalents, at Carrying Value	$ 587,589	$ 642,570	$ 587,589	$ 642,570	$ 697,424			$ 917,822
Cash and due from banks, Fair Value	587,589	642,570	587,589	642,570	697,424
Available-for-sale Securities, Carrying Amount	3,838,509	3,478,420	3,838,509	3,478,420	3,545,288
Held-to-maturity Securities, Amortized Cost before Other than Temporary Impairment	2,787,513	3,052,118	2,787,513	3,052,118	2,903,609
Held-to-maturity Securities, Carrying Amount		3,052,118		3,052,118	2,903,609
Held-to-maturity Securities, Fair Value	2,760,120	3,001,866	2,760,120	3,001,866	2,875,920
Other Investments, Carrying Amount	147,967	148,433	147,967	148,433	148,654
Other Investments, Fair Value	147,967	148,433	147,967	148,433	148,654
Loans Receivable Held-for-sale, Carrying Amount	5,432	21,632	5,432	21,632	13,428
Loans Held-for-sale, Fair Value Disclosure	8,302	21,632	8,302	21,632	14,389
Loans and Leases Receivable, Net Amount	15,556,851	14,827,591	15,556,851	14,827,591	15,182,498
Originated loans and leases receivable, carrying value		11,375,243		11,375,243	12,398,116
Net noncovered loans, Fair Value	13,077,485	11,458,318	13,077,485	11,458,318	12,235,530
Net covered loans and loss share receivable, Carrying Amount		433,538		433,538	312,659
Net covered loans and loss share receivable, Fair Value	211,887	433,538	211,887	433,538	312,659
Accrued interest receivable, Carrying Amount	66,501	63,172	66,501	63,172	63,657
Accrued interest receivable, Fair Value	66,501	63,172	66,501	63,172	63,657
Derivative Assets, Carrying Amount	48,073	50,550	48,073	50,550	55,197
Derivative Asset, Fair Value, Gross Asset	48,073	50,550	48,073	50,550	55,197
Financial liabilities:
Deposits, Carrying Amount	19,673,850	19,298,396	19,673,850	19,298,396	19,504,665
Deposits, Fair Value	19,681,270	19,300,842	19,681,270	19,300,842	19,510,192
Total Federal funds purchased and securities sold under agreements to repurchase, Carrying Amount	1,519,250	1,218,855	1,519,250	1,218,855	1,272,591
Federal funds purchased and securities sold under agreements to repurchase, Fair Value	1,519,250	1,218,855	1,519,250	1,218,855	1,272,591
Wholesale Borrowings, Carrying Amount	366,074	649,021	366,074	649,021	428,071
Other Borrowings, Fair Value	369,337	652,615	369,337	652,615	430,676
Long-term Debt	497,393	324,433	497,393	324,433	505,192
Long-term Debt, Fair Value	509,900	335,757	509,900	335,757	516,476
Accrued interest payable, Carrying Amount	9,910	8,311	9,910	8,311	9,820
Accrued interest payable, Fair Value	9,910	8,311	9,910	8,311	9,820
Derivative liabilities, Carrying Amount	51,497	57,544	51,497	57,544	55,439
Derivative Liability, Fair Value, Gross Liability	51,497	57,544	51,497	57,544	55,439
Mortgage Servicing rights Valuation Allowance	(490)	(562)	(490)	(562)	(955)	$ (1,131)	$ (425)	$ (282)
Mortgage Servicing Rights Net Carrying balance	20,145	21,588	20,145	21,588	21,100
Mortgage Servicing Rights (MSR) Impairment (Recovery)	641	137	(465)	280	(700)
Impaired Collateral Dependant Loans, Recorded Investment	82,700	62,200	82,700	62,200	60,300
Determination Of Specific Allowance For Loan Losses	(10,200)	(6,200)	(10,200)	(6,200)	(4,300)
Fair Value, Inputs, Level 1
Financial assets:
Cash and due from banks, Fair Value		642,570		642,570	697,424
Available-for-sale Securities, Carrying Amount	2,824	2,935	2,824	2,935	2,974
Held-to-maturity Securities, Fair Value	0	0	0	0	0
Other Investments, Fair Value	0	0	0	0	0
Loans Held-for-sale, Fair Value Disclosure	0	0	0	0	0
Net noncovered loans, Fair Value	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	3,524,149	3,124,752	3,524,149	3,124,752	3,203,127
Held-to-maturity Securities, Fair Value		3,001,866		3,001,866	2,875,920
Other Investments, Fair Value		148,433		148,433	148,654
Loans Held-for-sale, Fair Value Disclosure	8,302	21,632	8,302	21,632	14,389
Net noncovered loans, Fair Value	0	0	0	0	0
Net covered loans and loss share receivable, Fair Value	0	0	0	0	0
Accrued interest receivable, Fair Value	66,501	63,172	66,501	63,172	63,657
Derivative Asset, Fair Value, Gross Asset	48,073	50,550	48,073	50,550	55,197
Financial liabilities:
Deposits, Fair Value	19,681,270	19,300,842	19,681,270	19,300,842	19,510,192
Federal funds purchased and securities sold under agreements to repurchase, Fair Value		1,218,855		1,218,855	1,272,591
Other Borrowings, Fair Value	369,337	652,615	369,337	652,615	430,676
Long-term Debt, Fair Value	509,900	335,757	509,900	335,757	516,476
Accrued interest payable, Fair Value	9,910	8,311	9,910	8,311	9,820
Derivative Liability, Fair Value, Gross Liability	51,497	57,544	51,497	57,544	55,439
Level 3
Financial assets:
Cash and due from banks, Fair Value	0	0	0	0	0
Available-for-sale Securities, Carrying Amount	311,536	350,733	311,536	350,733	339,187
Held-to-maturity Securities, Fair Value	0	0	0	0	0
Other Investments, Fair Value	0	0	0	0	0
Loans Held-for-sale, Fair Value Disclosure	0	0	0	0	0
Loans and Leases Receivable, Net Amount		3,166,228		3,166,228
Net noncovered loans, Fair Value	13,077,485	11,458,318	13,077,485	11,458,318	12,235,530
Net covered loans and loss share receivable, Fair Value	211,887	433,538	211,887	433,538	312,659
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	13,254,230	11,375,243	13,254,230	11,375,243	12,398,116
Acquired Loans
Financial assets:
Loans and Leases Receivable, Net Amount	2,090,734	3,018,810	2,090,734	3,018,810	2,471,723
Net noncovered loans, Fair Value	2,167,304	3,166,228	2,167,304	3,166,228	2,564,842
Acquired Loans | Fair Value, Inputs, Level 1
Financial assets:
Net noncovered loans, Fair Value	0	0	0	0	0
Acquired Loans | Fair Value, Inputs, Level 2
Financial assets:
Net noncovered loans, Fair Value	0	$ 0	0	$ 0	0
Acquired Loans | Level 3
Financial assets:
Net noncovered loans, Fair Value	$ 2,167,304		$ 2,167,304		$ 2,564,842