Fair Value Measurement (Fair Value Disclosure by Balance Sheet Grouping ) (Details) (USD $)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013	Jun. 30, 2014	Jun. 30, 2013	Dec. 31, 2012
Financial assets:
Cash and Cash Equivalents, at Carrying Value	$ 485,328,000	$ 1,247,267,000	$ 485,328,000	$ 1,247,267,000	$ 917,822,000			$ 258,014,000
Cash and due from banks, Fair Value	485,328,000	1,247,267,000	485,328,000	1,247,267,000	917,822,000
Available-for-sale Securities, Carrying Amount	3,462,990,000	3,256,259,000	3,462,990,000	3,256,259,000	3,273,174,000
Held-to-maturity Securities, Amortized Cost before Other than Temporary Impairment	3,002,262,000	2,749,934,000	3,002,262,000	2,749,934,000	2,935,688,000
Held-to-maturity Securities, Carrying Amount		2,749,934,000		2,749,934,000	2,935,688,000
Held-to-maturity Securities, Fair Value	2,947,172,000	2,658,433,000	2,947,172,000	2,658,433,000	2,824,240,000
Other Investments, Carrying Amount	148,421,000	270,369,000	148,421,000	270,369,000	180,803,000
Other Investments, Fair Value	148,421,000	270,369,000	148,421,000	270,369,000	180,803,000
Loans Receivable Held-for-sale, Carrying Amount	19,512,000	17,813,000	19,512,000	17,813,000	11,622,000
Loans Held-for-sale, Fair Value Disclosure	19,512,000	17,813,000	19,512,000	17,813,000	11,622,000
Loans and Leases Receivable, Net Amount	15,101,949,000	14,117,001,000	15,101,949,000	14,117,001,000	14,159,720,000
Loans and Leases Receivable, Carrying Amount		9,690,848,000		9,690,848,000	10,116,903,000
Net noncovered loans, Fair Value	11,995,816,000	9,623,848,000	11,995,816,000	9,623,848,000	10,017,722,000
Net covered loans and loss share receivable, Carrying Amount		608,732,000		608,732,000	547,943,000
Net covered loans and loss share receivable, Fair Value	382,175,000	608,732,000	382,175,000	608,732,000	547,943,000
Accrued interest receivable, Carrying Amount	65,736,000	49,820,000	65,736,000	49,820,000	52,929,000
Accrued interest receivable, Fair Value	65,736,000	49,820,000	65,736,000	49,820,000	52,929,000
Derivative Assets, Carrying Amount	43,097,000	53,839,000	43,097,000	53,839,000	47,902,000
Derivative Asset, Fair Value, Gross Asset	43,097,000	53,839,000	43,097,000	53,839,000	47,902,000
Financial liabilities:
Deposits, Carrying Amount	19,366,911,000	19,489,533,000	19,366,911,000	19,489,533,000	19,533,601,000
Deposits, Fair Value	19,370,624,000	19,508,531,000	19,370,624,000	19,508,531,000	19,532,368,000
Total Federal funds purchased and securities sold under agreements to repurchase, Carrying Amount	1,273,290,000	1,049,801,000	1,273,290,000	1,049,801,000	851,535,000
Federal funds purchased and securities sold under agreements to repurchase, Fair Value	1,273,290,000	1,049,801,000	1,273,290,000	1,049,801,000	851,535,000
Wholesale Borrowings, Carrying Amount	608,463,000	200,858,000	608,463,000	200,858,000	200,600,000
Other Borrowings, Fair Value	611,753,000	204,461,000	611,753,000	204,461,000	204,124,000
Long-term Debt	249,933,000	324,425,000	249,933,000	324,425,000	324,428,000
Long-term Debt, Fair Value	259,051,000	321,255,000	259,051,000	321,255,000	319,711,000
Accrued interest payable, Carrying Amount	5,310,000	5,884,000	5,310,000	5,884,000	9,339,000
Accrued interest payable, Fair Value	5,310,000	5,884,000	5,310,000	5,884,000	9,339,000
Derivative liabilities, Carrying Amount	49,280,000	65,506,000	49,280,000	65,506,000	58,201,000
Derivative Liability, Fair Value, Gross Liability	49,280,000	65,506,000	49,280,000	65,506,000	58,201,000
Mortgage Servicing rights Valuation Allowance	(505,000)	572,000	(505,000)	572,000	(282,000)	(562,000)	(482,000)	2,564,000
Mortgage Servicing Rights Net Carrying balance	21,684,000	22,351,000	21,684,000	22,351,000	22,500,000
Mortgage Servicing Rights (MSR) Impairment (Recovery)	57,000	(90,000)	(223,000)	(1,992,000)	2,300,000
Impaired Collateral Dependant Loans, Recorded Investment	59,900,000	51,300,000	59,900,000	51,300,000	52,600,000
Determination Of Specific Allowance For Loan Losses	(4,500,000)	(3,100,000)	(4,500,000)	(3,100,000)	(4,800,000)
Fair Value, Inputs, Level 1
Financial assets:
Cash and due from banks, Fair Value		1,247,267,000		1,247,267,000	917,822,000
Available-for-sale Securities, Carrying Amount	2,916,000	3,096,000	2,916,000	3,096,000	3,036,000
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	3,112,553,000	2,930,401,000	3,112,553,000	2,930,401,000	2,922,527,000
Held-to-maturity Securities, Fair Value		2,658,433,000		2,658,433,000	2,824,240,000
Other Investments, Fair Value		270,369,000		270,369,000	180,803,000
Loans Held-for-sale, Fair Value Disclosure	19,512,000	17,813,000	19,512,000	17,813,000	11,622,000
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	65,736,000	49,820,000	65,736,000	49,820,000	52,929,000
Derivative Asset, Fair Value, Gross Asset	43,097,000	53,839,000	43,097,000	53,839,000	47,902,000
Financial liabilities:
Deposits, Fair Value	19,370,624,000	19,508,531,000	19,370,624,000	19,508,531,000	19,532,368,000
Federal funds purchased and securities sold under agreements to repurchase, Fair Value		1,049,801,000		1,049,801,000	851,535,000
Other Borrowings, Fair Value	611,753,000	204,461,000	611,753,000	204,461,000	204,124,000
Long-term Debt, Fair Value	259,051,000	321,255,000	259,051,000	321,255,000	319,711,000
Accrued interest payable, Fair Value	5,310,000	5,884,000	5,310,000	5,884,000	9,339,000
Derivative Liability, Fair Value, Gross Liability	48,765,000	65,506,000	48,765,000	65,506,000	58,201,000
Level 3
Financial assets:
Cash and due from banks, Fair Value	0	0	0	0	0
Available-for-sale Securities, Carrying Amount	347,521,000	322,762,000	347,521,000	322,762,000	347,611,000
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	11,995,816,000	9,623,848,000	11,995,816,000	9,623,848,000	10,017,722,000
Net covered loans and loss share receivable, Fair Value	382,175,000	608,732,000	382,175,000	608,732,000	547,943,000
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	515,000	0	515,000	0	0
Originated Loans
Financial assets:
Loans and Leases Receivable, Net Amount	11,980,876,000	9,690,848,000	11,980,876,000	9,690,848,000	10,116,903,000
Acquired Loans
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Loans Receivable, Fair Value Disclosure					3,627,275,000
Financial assets:
Loans and Leases Receivable, Net Amount	2,738,898,000	3,817,421,000	2,738,898,000	3,817,421,000	3,494,874,000
Net noncovered loans, Fair Value	2,869,303,000	3,817,421,000	2,869,303,000	3,817,421,000
Acquired Loans | Fair Value, Inputs, Level 1
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Loans Receivable, Fair Value Disclosure					0
Financial assets:
Net noncovered loans, Fair Value	0	0	0	0
Acquired Loans | Fair Value, Inputs, Level 2
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Loans Receivable, Fair Value Disclosure					0
Financial assets:
Net noncovered loans, Fair Value	0	0	0	0
Acquired Loans | Level 3
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Loans Receivable, Fair Value Disclosure					3,627,275,000
Financial assets:
Net noncovered loans, Fair Value	$ 2,869,303,000		$ 2,869,303,000