XML 130 R63.htm IDEA: XBRL DOCUMENT
v3.19.3.a.u2

Loans Held for Sale and Loan Servicing Rights (Activity in Capitalized Mortgage Serving Assets) (Details) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Loans Held For Sale And Loan Servicing Rights [Abstract] |  |  |
Mortgage servicing assets, beginning of year | $ 1,021 | $ 990 | $ 1,077
Originations | 349 | 298 | 231
Amortization | (242) | (267) | (318)
Mortgage servicing assets, end of year | 1,128 | 1,021 | 990
Mortgage servicing assets, net, end of year | $ 1,128 | $ 1,021 | $ 990

X
- Definition LoansHeldForSaleAndLoanServicingRightsAbstract. + References No definition available. + Details
Name: | fisi_LoansHeldForSaleAndLoanServicingRightsAbstract
Namespace Prefix: | fisi_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Mortgage Servicing Assets, Before Valuation Allowance + References No definition available. + Details
Name: | fisi_MortgageServicingAssetsBeforeValuationAllowance
Namespace Prefix: | fisi_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Mortgage Servicing Assets Net Of Valuation Allowance + References No definition available. + Details
Name: | fisi_MortgageServicingAssetsNetOfValuationAllowance
Namespace Prefix: | fisi_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition The periodic amortization (in proportion to and over the period of estimated net servicing income or loss) of capitalized servicing rights, which contractually entitle the servicer to receive fees and ancillary revenues for performing billing, collection, disbursement and recordkeeping services in connection with a mortgage portfolio. As a noncash expense, this element is added back to net income when calculating cash provided by or used in operations using the indirect method. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3602-108585 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 860 -SubTopic 50 -Section 50 -Paragraph 4 -Subparagraph (a)(4) -URI http://asc.fasb.org/extlink&oid=116651436&loc=d3e122739-111746 + Details
Name: | us-gaap_AmortizationOfMortgageServicingRightsMSRs
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition The value of new servicing assets, subsequently measured at fair value, acquired or created during the current period through purchases or from transfers of financial assets. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 860 -SubTopic 50 -Section 50 -Paragraph 3 -Subparagraph (a)(2) -URI http://asc.fasb.org/extlink&oid=116651436&loc=d3e122625-111746 + Details
Name: | us-gaap_ServicingAssetAtFairValueAdditions
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration