Fair Value Measurement (Recurring and Nonrecurring Table) (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
True-up Liabitlity Discount Rate	3.51%	3.31%
True-up Liability Effect of Change in Discount Rate By One Percent	$ 600	$ (600)
Collateral Dependant Impaired and Non Accrual Loans Carrying Amount	80,400	55,400	$ 56,000
Recurring Fair Value Measurements
Available-for-sale	3,925,724	3,462,990	3,545,288
Residential loans held for sale	7,781	19,512	14,389
Derivative Asset, Fair Value, Gross Asset	76,196	43,097	55,197
Total Assets, Fair Value Disclosure, Recurring	4,009,701	3,525,599	3,614,874
Derivative Liability, Fair Value, Gross Liability	67,936	49,280	55,439
True Up Liability	13,572	12,804	13,294
Total liabilities at fair value on a recurring basis	81,508	62,084	68,733
Nonrecurring Fair Value Measurements [Abstract]
Fair Value of Mortgage Servicing Rights	19,556	22,229	21,228
Impaired and Non Accrual Loans Fair Value Disclosure	80,386	55,406	56,041
Other Real Estate, Non Covered	16,050	14,896	12,510
Other Real Estate Covered by Loss Share		5,798	3,614
Nonrecurring Fair Value	115,992	98,329	93,393
Impairment of Noncovered Other Real Estate Owned		700	2,600
Impairment of Covered Other Real Esate Owned		100	1,200
Foreclosed Real Estate Expense	400
Level 1
Recurring Fair Value Measurements
Available-for-sale	2,781	2,916	2,974
Residential loans held for sale	0	0	0
Derivative Asset, Fair Value, Gross Asset	0	0	0
Total Assets, Fair Value Disclosure, Recurring	2,781	2,916	2,974
Derivative Liability, Fair Value, Gross Liability	0	0	0
True Up Liability	0	0	0
Total liabilities at fair value on a recurring basis	0	0	0
Nonrecurring Fair Value Measurements [Abstract]
Fair Value of Mortgage Servicing Rights	0	0	0
Impaired and Non Accrual Loans Fair Value Disclosure	0	0	0
Other Real Estate, Non Covered	0	0	0
Other Real Estate Covered by Loss Share		0	0
Nonrecurring Fair Value	0	0	0
Level 2
Recurring Fair Value Measurements
Available-for-sale	3,575,950	3,112,553	3,203,127
Residential loans held for sale	7,781	19,512	14,389
Derivative Asset, Fair Value, Gross Asset	76,196	43,097	55,197
Total Assets, Fair Value Disclosure, Recurring	3,659,927	3,175,162	3,272,713
Derivative Liability, Fair Value, Gross Liability	67,936	48,765	55,439
True Up Liability	0	0	0
Total liabilities at fair value on a recurring basis	67,936	48,765	55,439
Nonrecurring Fair Value Measurements [Abstract]
Fair Value of Mortgage Servicing Rights	0	0	0
Impaired and Non Accrual Loans Fair Value Disclosure	0	0	0
Other Real Estate, Non Covered	0	0	0
Other Real Estate Covered by Loss Share		0	0
Nonrecurring Fair Value	0	0	0
Level 3
Recurring Fair Value Measurements
Available-for-sale	346,993	347,521	339,187
Residential loans held for sale	0	0	0
Derivative Asset, Fair Value, Gross Asset	0	0	0
Total Assets, Fair Value Disclosure, Recurring	346,993	347,521	339,187
Derivative Liability, Fair Value, Gross Liability	0	515	0
True Up Liability	13,572	12,804	13,294
Total liabilities at fair value on a recurring basis	13,572	13,319	13,294
Nonrecurring Fair Value Measurements [Abstract]
Fair Value of Mortgage Servicing Rights	19,556	22,229	21,228
Impaired and Non Accrual Loans Fair Value Disclosure	80,386	55,406	56,041
Other Real Estate, Non Covered	16,050	14,896	12,510
Other Real Estate Covered by Loss Share		5,798	3,614
Nonrecurring Fair Value	115,992	98,329	93,393
US Treasury Securities
Recurring Fair Value Measurements
Available-for-sale	5,005
US Treasury Securities | Level 2
Recurring Fair Value Measurements
Available-for-sale	5,005
Equity Securities
Recurring Fair Value Measurements
Available-for-sale	2,781	2,916	2,974
Equity Securities | Level 1
Recurring Fair Value Measurements
Available-for-sale		2,916	2,974
Equity Securities | Level 2
Recurring Fair Value Measurements
Available-for-sale	0	0	0
Equity Securities | Level 3
Recurring Fair Value Measurements
Available-for-sale	0	0	0
Marketable Securities and Investments Held at Cost
Recurring Fair Value Measurements
Available-for-sale		2,916	2,974
Marketable Securities and Investments Held at Cost | Level 1
Recurring Fair Value Measurements
Available-for-sale	2,781
Non-marketable Equity Securities
Recurring Fair Value Measurements
Available-for-sale		2,500
Non-marketable Equity Securities | Level 2
Recurring Fair Value Measurements
Available-for-sale		0
Non-marketable Equity Securities | Level 3
Recurring Fair Value Measurements
Available-for-sale		2,500
US Government Agencies Debt Securities
Recurring Fair Value Measurements
Available-for-sale	2,516		2,482
US Government Agencies Debt Securities | Level 2
Recurring Fair Value Measurements
Available-for-sale	2,516
U.S. States and political subdivisions debt securities
Recurring Fair Value Measurements
Available-for-sale	200,810	237,067	227,342
U.S. States and political subdivisions debt securities | Level 1
Recurring Fair Value Measurements
Available-for-sale	0	0	0
U.S. States and political subdivisions debt securities | Level 2
Recurring Fair Value Measurements
Available-for-sale	200,810	237,067	227,342
U.S. States and political subdivisions debt securities | Level 3
Recurring Fair Value Measurements
Available-for-sale	0	0	0
Residential Mortgage Backed Securities Issued by US Government Sponsored Enterprises
Recurring Fair Value Measurements
Available-for-sale	945,624	996,387	970,998
Residential Mortgage Backed Securities Issued by US Government Sponsored Enterprises | Level 1
Recurring Fair Value Measurements
Available-for-sale	0	0	0
Residential Mortgage Backed Securities Issued by US Government Sponsored Enterprises | Level 2
Recurring Fair Value Measurements
Available-for-sale	945,624	996,387	970,998
Residential Mortgage Backed Securities Issued by US Government Sponsored Enterprises | Level 3
Recurring Fair Value Measurements
Available-for-sale	0	0	0
Commercial Mortgage Backed Securities Issued by US Government Sponsored Enterprises
Recurring Fair Value Measurements
Available-for-sale	155,076	84,764	103,403
Commercial Mortgage Backed Securities Issued by US Government Sponsored Enterprises | Level 1
Recurring Fair Value Measurements
Available-for-sale	0	0	0
Commercial Mortgage Backed Securities Issued by US Government Sponsored Enterprises | Level 2
Recurring Fair Value Measurements
Available-for-sale	155,076	84,764	103,403
Commercial Mortgage Backed Securities Issued by US Government Sponsored Enterprises | Level 3
Recurring Fair Value Measurements
Available-for-sale	0	0	0
Residential Collateralized Mortgage-Backed Securities Issued by US Government Sponsored Enterprises
Recurring Fair Value Measurements
Available-for-sale	2,022,959	1,600,317	1,676,567
Residential Collateralized Mortgage-Backed Securities Issued by US Government Sponsored Enterprises | Level 1
Recurring Fair Value Measurements
Available-for-sale	0	0	0
Residential Collateralized Mortgage-Backed Securities Issued by US Government Sponsored Enterprises | Level 2
Recurring Fair Value Measurements
Available-for-sale	2,022,959	1,600,317	1,676,567
Residential Collateralized Mortgage-Backed Securities Issued by US Government Sponsored Enterprises | Level 3
Recurring Fair Value Measurements
Available-for-sale	0	0	0
Residential Collateralized Mortgage-Backed Securities Issued by Non-US Government Agency
Recurring Fair Value Measurements
Available-for-sale	5	7	7
Residential Collateralized Mortgage-Backed Securities Issued by Non-US Government Agency | Level 1
Recurring Fair Value Measurements
Available-for-sale	0	0	0
Residential Collateralized Mortgage-Backed Securities Issued by Non-US Government Agency | Level 2
Recurring Fair Value Measurements
Available-for-sale	0	1	1
Residential Collateralized Mortgage-Backed Securities Issued by Non-US Government Agency | Level 3
Recurring Fair Value Measurements
Available-for-sale	5	6	6
Commercial Collateralized Mortgage Backed Securities Issued by US Government Sponsored Enterprises
Recurring Fair Value Measurements
Available-for-sale	243,960	194,017	222,334
Commercial Collateralized Mortgage Backed Securities Issued by US Government Sponsored Enterprises | Level 1
Recurring Fair Value Measurements
Available-for-sale	0	0	0
Commercial Collateralized Mortgage Backed Securities Issued by US Government Sponsored Enterprises | Level 2
Recurring Fair Value Measurements
Available-for-sale	243,960	194,017	222,334
Commercial Collateralized Mortgage Backed Securities Issued by US Government Sponsored Enterprises | Level 3
Recurring Fair Value Measurements
Available-for-sale	0	0	0
Corporate debt securities
Recurring Fair Value Measurements
Available-for-sale	54,537	54,594	51,337
Corporate debt securities | Level 1
Recurring Fair Value Measurements
Available-for-sale	0	0	0
Corporate debt securities | Level 2
Recurring Fair Value Measurements
Available-for-sale	0	0	0
Corporate debt securities | Level 3
Recurring Fair Value Measurements
Available-for-sale		54,594	51,337
Collateralized Loan Obligations
Recurring Fair Value Measurements
Available-for-sale	292,451	290,421	287,844
Collateralized Loan Obligations | Level 1
Recurring Fair Value Measurements
Available-for-sale	0	0	0
Collateralized Loan Obligations | Level 2
Recurring Fair Value Measurements
Available-for-sale	0	0	0
Collateralized Loan Obligations | Level 3
Recurring Fair Value Measurements
Available-for-sale		290,421	287,844
Not Designated as Hedging Instrument
Recurring Fair Value Measurements
Derivative Asset, Fair Value, Gross Asset	63,586	43,097	49,941
Derivative Liability, Fair Value, Gross Liability	63,358	41,696	48,756
Interest Rate Swap | Designated as Hedging Instrument
Recurring Fair Value Measurements
Derivative Asset, Fair Value, Gross Asset	12,610	0	5,256
Derivative Liability, Fair Value, Gross Liability	4,578	7,584	6,683
Interest Rate Swap | Designated as Hedging Instrument | Level 1
Recurring Fair Value Measurements
Derivative Asset, Fair Value, Gross Asset	0	0	0
Derivative Liability, Fair Value, Gross Liability	0	0	0
Interest Rate Swap | Designated as Hedging Instrument | Level 2
Recurring Fair Value Measurements
Derivative Asset, Fair Value, Gross Asset	12,610	0	5,256
Derivative Liability, Fair Value, Gross Liability	4,578	7,584	6,683
Interest Rate Swap | Designated as Hedging Instrument | Level 3
Recurring Fair Value Measurements
Derivative Asset, Fair Value, Gross Asset	0	0	0
Derivative Liability, Fair Value, Gross Liability	0	0	0
Interest Rate Swap | Not Designated as Hedging Instrument
Recurring Fair Value Measurements
Derivative Asset, Fair Value, Gross Asset	63,171	40,937	48,366
Derivative Liability, Fair Value, Gross Liability	63,171	40,937	48,366
Interest Rate Swap | Not Designated as Hedging Instrument | Level 1
Recurring Fair Value Measurements
Derivative Asset, Fair Value, Gross Asset	0	0	0
Derivative Liability, Fair Value, Gross Liability	0	0	0
Interest Rate Swap | Not Designated as Hedging Instrument | Level 2
Recurring Fair Value Measurements
Derivative Asset, Fair Value, Gross Asset	63,171	40,937	48,366
Derivative Liability, Fair Value, Gross Liability	63,171	40,937	48,366
Interest Rate Swap | Not Designated as Hedging Instrument | Level 3
Recurring Fair Value Measurements
Derivative Asset, Fair Value, Gross Asset	0	0	0
Derivative Liability, Fair Value, Gross Liability	0	0	0
Mortgage Loan Commitments | Not Designated as Hedging Instrument
Recurring Fair Value Measurements
Derivative Asset, Fair Value, Gross Asset	279	1,975	1,408
Derivative Liability, Fair Value, Gross Liability	0	0	0
Mortgage Loan Commitments | Not Designated as Hedging Instrument | Level 1
Recurring Fair Value Measurements
Derivative Asset, Fair Value, Gross Asset	0	0	0
Mortgage Loan Commitments | Not Designated as Hedging Instrument | Level 2
Recurring Fair Value Measurements
Derivative Asset, Fair Value, Gross Asset	279	1,975	1,408
Mortgage Loan Commitments | Not Designated as Hedging Instrument | Level 3
Recurring Fair Value Measurements
Derivative Asset, Fair Value, Gross Asset	0	0	0
Forward sales contracts | Not Designated as Hedging Instrument
Recurring Fair Value Measurements
Derivative Asset, Fair Value, Gross Asset		0	0
Derivative Liability, Fair Value, Gross Liability	75	91	272
Forward sales contracts | Not Designated as Hedging Instrument | Level 1
Recurring Fair Value Measurements
Derivative Asset, Fair Value, Gross Asset		0	0
Derivative Liability, Fair Value, Gross Liability	0	0	0
Forward sales contracts | Not Designated as Hedging Instrument | Level 2
Recurring Fair Value Measurements
Derivative Asset, Fair Value, Gross Asset	0	0	0
Derivative Liability, Fair Value, Gross Liability	75	91	272
Forward sales contracts | Not Designated as Hedging Instrument | Level 3
Recurring Fair Value Measurements
Derivative Asset, Fair Value, Gross Asset		0	0
Derivative Liability, Fair Value, Gross Liability	0	0	0
Foreign Exchange | Not Designated as Hedging Instrument
Recurring Fair Value Measurements
Derivative Asset, Fair Value, Gross Asset	136	185	167
Derivative Liability, Fair Value, Gross Liability	112	153	118
Foreign Exchange | Not Designated as Hedging Instrument | Level 1
Recurring Fair Value Measurements
Derivative Asset, Fair Value, Gross Asset	0	0	0
Derivative Liability, Fair Value, Gross Liability	0	0	0
Foreign Exchange | Not Designated as Hedging Instrument | Level 2
Recurring Fair Value Measurements
Derivative Asset, Fair Value, Gross Asset	136	185	167
Derivative Liability, Fair Value, Gross Liability	112	153	118
Foreign Exchange | Not Designated as Hedging Instrument | Level 3
Recurring Fair Value Measurements
Derivative Asset, Fair Value, Gross Asset	0	0	0
Derivative Liability, Fair Value, Gross Liability	0	0	0
Equity Swap | Not Designated as Hedging Instrument
Recurring Fair Value Measurements
Derivative Asset, Fair Value, Gross Asset	0	0	0
Derivative Liability, Fair Value, Gross Liability		515	0
Equity Swap | Not Designated as Hedging Instrument | Level 1
Recurring Fair Value Measurements
Derivative Liability, Fair Value, Gross Liability		0
Equity Swap | Not Designated as Hedging Instrument | Level 2
Recurring Fair Value Measurements
Derivative Liability, Fair Value, Gross Liability		0
Equity Swap | Not Designated as Hedging Instrument | Level 3
Recurring Fair Value Measurements
Derivative Liability, Fair Value, Gross Liability	0	515
Credit Risk Contract | Not Designated as Hedging Instrument
Recurring Fair Value Measurements
Derivative Asset, Fair Value, Gross Asset	0	0	0
Derivative Liability, Fair Value, Gross Liability	$ 0	$ 0	$ 0