Goodwill, Core Deposit Premium and Other Intangible Assets (Mortgage and commercial loans servicing) (Details) - USD ($)	3 Months Ended	12 Months Ended
Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
Valuation servicing rights in tranches [Line Items]
Mortgage loans serviced for others	$ 4,110,000,000		$ 4,060,000,000
Custodial escrow balances maintained	25,000,000		19,200,000
Valuation allowance	0		0
Mortgage Servicing Rights
Valuation servicing rights in tranches [Line Items]
Servicing asset at amortized value	$ 38,944,000	$ 34,492,000	$ 40,900,000
Prepayment rate	12.09%		10.65%
Discount rate	9.26%		9.25%
Fees collected for servicing of mortgage loans	$ 2,900,000	2,500,000
Mortgage Servicing Rights \| Minimum
Valuation servicing rights in tranches [Line Items]
Average cap rate	0.88%		0.65%
Mortgage Servicing Rights \| Maximum
Valuation servicing rights in tranches [Line Items]
Average cap rate	1.35%		1.38%
Mortgage Servicing Rights 15-year Tranche
Valuation servicing rights in tranches [Line Items]
Servicing asset, agreement term	15 years
Mortgage Servicing Rights 30-year Tranche
Valuation servicing rights in tranches [Line Items]
Servicing asset, agreement term	30 years
Commercial Servicing Rights
Valuation servicing rights in tranches [Line Items]
Servicing asset at amortized value	$ 4,899,000	$ 4,429,000
Fees collected for servicing of mortgage loans	80,000
Loans serviced for Small Business Administration and US Department of Agriculture	$ 189,900,000
Commercial Servicing Rights \| Minimum
Valuation servicing rights in tranches [Line Items]
Prepayment rate	7.14%		7.33%
Discount rate	11.74%		12.35%
Average cap rate	0.031%		0.018%
Commercial Servicing Rights \| Maximum
Valuation servicing rights in tranches [Line Items]
Prepayment rate	8.10%		8.10%
Discount rate	13.49%		13.49%
Average cap rate	0.0445%		0.0445%

Mortgage Loans Serviced for Others, Amount

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- Definition

Servicing Asset, Agreement Term

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No definition available.

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- Definition

Valuation servicing rights in tranches [Line Items]

+ References

No definition available.

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- Definition

The designation of funds furnished by a borrower to a lender to assure future payments of the borrower's real estate taxes and insurance obligations with respect to a mortgaged property. Escrow deposits may be made for a variety of other purposes such as earnest money and contingent payments. This element excludes replacement reserves which are an escrow separately provided for within the US GAAP taxonomy.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.10)
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

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- Definition

Ratio of the net operating income produced by an asset and its capital cost (original prices paid to buy the asset), used as an input to measure fair value.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (bbb)
-URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258

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Interest rate used to find the present value of an amount to be paid or received in the future as an input to measure fair value. For example, but not limited to, weighted average cost of capital (WACC), cost of capital, cost of equity and cost of debt.

+ References

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Rate at which loans or a loan portfolio are expected to prepay principal balances, used as an input to measure fair value.

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- Definition

Income from mortgage banking activities (fees and commissions) and servicing real estate mortgages, credit cards, and other financial assets held by others net of any related impairment of capitalized service costs. Also includes any premiums received in lieu of regular servicing fees on such loans only as earned over the life of the loans.

+ References

No definition available.

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- Definition

Aggregate amount of servicing assets that are subsequently measured at fair value and servicing assets that are subsequently measured using the amortization method.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 50
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6469459&loc=d3e122501-111745

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- Definition

Fair value of contract to service financial assets under which the benefits of servicing are expected to more than adequately compensate the servicer.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 50
-Section 50
-Paragraph 4
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=56950315&loc=d3e122739-111746

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 20
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=7516967&loc=d3e66267-113978

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Amount of valuation allowance applied to contract to service financial assets under which the benefits of servicing are expected to more than adequately compensate the servicer.

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