Mortgage Servicing Rights - At Amortized Cost (Details) (Mortgage loans, USD $)
In Thousands, unless otherwise specified |
12 Months Ended | ||
---|---|---|---|
Dec. 31, 2014
|
Dec. 31, 2013
|
Dec. 31, 2012
|
|
Mortgage loans
|
|||
Servicing Asset at Amortized Value, Balance [Roll Forward] | |||
Servicing asset at amortized cost, before valuation reserve, beginning | $ 14,018fibk_ServicingAssetAtAmortizedCostBeforeValuationReserve / us-gaap_FinancialInstrumentAxis = fibk_MortgageLoansMember |
$ 13,224fibk_ServicingAssetAtAmortizedCostBeforeValuationReserve / us-gaap_FinancialInstrumentAxis = fibk_MortgageLoansMember |
$ 13,450fibk_ServicingAssetAtAmortizedCostBeforeValuationReserve / us-gaap_FinancialInstrumentAxis = fibk_MortgageLoansMember |
Sales of mortgage servicing rights | 0us-gaap_ServicingAssetAtAmortizedValueDisposals / us-gaap_FinancialInstrumentAxis = fibk_MortgageLoansMember |
0us-gaap_ServicingAssetAtAmortizedValueDisposals / us-gaap_FinancialInstrumentAxis = fibk_MortgageLoansMember |
(735)us-gaap_ServicingAssetAtAmortizedValueDisposals / us-gaap_FinancialInstrumentAxis = fibk_MortgageLoansMember |
Originations of mortgage servicing rights | 2,717fibk_ServicingAssetAtAmortizedValueOriginations / us-gaap_FinancialInstrumentAxis = fibk_MortgageLoansMember |
3,581fibk_ServicingAssetAtAmortizedValueOriginations / us-gaap_FinancialInstrumentAxis = fibk_MortgageLoansMember |
4,563fibk_ServicingAssetAtAmortizedValueOriginations / us-gaap_FinancialInstrumentAxis = fibk_MortgageLoansMember |
Amorization expense | (2,361)us-gaap_ServicingAssetAtAmortizedValueAmortization1 / us-gaap_FinancialInstrumentAxis = fibk_MortgageLoansMember |
(2,787)us-gaap_ServicingAssetAtAmortizedValueAmortization1 / us-gaap_FinancialInstrumentAxis = fibk_MortgageLoansMember |
(3,501)us-gaap_ServicingAssetAtAmortizedValueAmortization1 / us-gaap_FinancialInstrumentAxis = fibk_MortgageLoansMember |
Write-off of permanent impairment | 0us-gaap_ServicingAssetAtAmortizedCostOtherThanTemporaryImpairments / us-gaap_FinancialInstrumentAxis = fibk_MortgageLoansMember |
0us-gaap_ServicingAssetAtAmortizedCostOtherThanTemporaryImpairments / us-gaap_FinancialInstrumentAxis = fibk_MortgageLoansMember |
(553)us-gaap_ServicingAssetAtAmortizedCostOtherThanTemporaryImpairments / us-gaap_FinancialInstrumentAxis = fibk_MortgageLoansMember |
Servicing asset at amortized cost, before valuation reserve, ending | 14,374fibk_ServicingAssetAtAmortizedCostBeforeValuationReserve / us-gaap_FinancialInstrumentAxis = fibk_MortgageLoansMember |
14,018fibk_ServicingAssetAtAmortizedCostBeforeValuationReserve / us-gaap_FinancialInstrumentAxis = fibk_MortgageLoansMember |
13,224fibk_ServicingAssetAtAmortizedCostBeforeValuationReserve / us-gaap_FinancialInstrumentAxis = fibk_MortgageLoansMember |
Less valuation reserve | (336)us-gaap_ValuationAllowanceForImpairmentOfRecognizedServicingAssetsBalance / us-gaap_FinancialInstrumentAxis = fibk_MortgageLoansMember |
(472)us-gaap_ValuationAllowanceForImpairmentOfRecognizedServicingAssetsBalance / us-gaap_FinancialInstrumentAxis = fibk_MortgageLoansMember |
(571)us-gaap_ValuationAllowanceForImpairmentOfRecognizedServicingAssetsBalance / us-gaap_FinancialInstrumentAxis = fibk_MortgageLoansMember |
Servicing asset at fair value, ending | 14,038us-gaap_ServicingAssetAtAmortizedValueFairValue / us-gaap_FinancialInstrumentAxis = fibk_MortgageLoansMember |
13,546us-gaap_ServicingAssetAtAmortizedValueFairValue / us-gaap_FinancialInstrumentAxis = fibk_MortgageLoansMember |
12,653us-gaap_ServicingAssetAtAmortizedValueFairValue / us-gaap_FinancialInstrumentAxis = fibk_MortgageLoansMember |
Principal balance of serviced loans underlying mortgage servicing rights | 2,615,311us-gaap_PrincipalAmountOutstandingOfLoansHeldInPortfolio / us-gaap_FinancialInstrumentAxis = fibk_MortgageLoansMember |
2,416,621us-gaap_PrincipalAmountOutstandingOfLoansHeldInPortfolio / us-gaap_FinancialInstrumentAxis = fibk_MortgageLoansMember |
2,146,351us-gaap_PrincipalAmountOutstandingOfLoansHeldInPortfolio / us-gaap_FinancialInstrumentAxis = fibk_MortgageLoansMember |
Mortgage servicing rights as a percentage of serviced loans | 0.0054fibk_ServicingAssetAsPercentageOfServicedLoansHeldInPortfolio / us-gaap_FinancialInstrumentAxis = fibk_MortgageLoansMember |
0.0056fibk_ServicingAssetAsPercentageOfServicedLoansHeldInPortfolio / us-gaap_FinancialInstrumentAxis = fibk_MortgageLoansMember |
0.0059fibk_ServicingAssetAsPercentageOfServicedLoansHeldInPortfolio / us-gaap_FinancialInstrumentAxis = fibk_MortgageLoansMember |
Disclosure of Transfer of Securitizations or Asset-backed Financing Financial Assets Accounted for as Sale | |||
Carrying value of sold mortgage servicing rights | 735fibk_TransfersOfFinancialAssetsAccountedForAsSaleCarryingValue / us-gaap_FinancialInstrumentAxis = fibk_MortgageLoansMember |
||
Losses on sale of mortgage servicing rights recorded as other expense | $ (19)us-gaap_SecuritizationFinancialAssetForWhichTransferIsAccountedAsSaleGainLossOnSale / us-gaap_FinancialInstrumentAxis = fibk_MortgageLoansMember |
X | ||||||||||
- Definition
Servicing Asset As a Percentage of Serviced Loans Held-In-Portfolio No definition available.
|
X | ||||||||||
- Definition
Servicing Asset at Amortized Cost, Before Valuation Reserve No definition available.
|
X | ||||||||||
- Definition
Servicing Asset at Amortized Value, Originations No definition available.
|
X | ||||||||||
- Definition
Transfers of Financial Assets Accounted for as Sale, Carrying Value No definition available.
|
X | ||||||||||
- Details
|
X | ||||||||||
- Definition
No authoritative reference available. Reference 1: http://www.xbrl.org/2003/role/presentationRef
|
X | ||||||||||
- Definition
No authoritative reference available. Reference 1: http://www.xbrl.org/2003/role/presentationRef
|
X | ||||||||||
- Definition
No authoritative reference available. Reference 1: http://www.xbrl.org/2003/role/presentationRef
|
X | ||||||||||
- Definition
No authoritative reference available. Reference 1: http://www.xbrl.org/2003/role/presentationRef
|
X | ||||||||||
- Details
|
X | ||||||||||
- Definition
No authoritative reference available. Reference 1: http://www.xbrl.org/2003/role/presentationRef
|
X | ||||||||||
- Definition
No authoritative reference available. Reference 1: http://www.xbrl.org/2003/role/presentationRef
|
X | ||||||||||
- Definition
No authoritative reference available. Reference 1: http://www.xbrl.org/2003/role/presentationRef
|