XML 82 R103.htm IDEA: XBRL DOCUMENT
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Fair Value of Assets and Liabilities Quantitative Information about Level 3 Fair Value Measurements (Details) (Nonrecurring Measurements, USD $) In Thousands, unless otherwise specified | 12 Months Ended
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Dec. 31, 2014 | Dec. 31, 2013
Quantitative Information About Level 3 Fair Value Measurements |  |  |  |
Fair Value | 18,480us-gaap_AssetsFairValueDisclosure |  | 29,558us-gaap_AssetsFairValueDisclosure |
Level 3 |  |  |  |
Quantitative Information About Level 3 Fair Value Measurements |  |  |  |
Fair Value | 18,480us-gaap_AssetsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember |  | 29,558us-gaap_AssetsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember |
Other real estate owned | Level 3 |  |  |  |
Quantitative Information About Level 3 Fair Value Measurements |  |  |  |
Fair Value | 3,000us-gaap_AssetsFairValueDisclosure / gbci_FairValueAssetsAndLiabilitiesByMajorTypesAxis = gbci_OtherRealEstateOwnedMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember |  | 10,888us-gaap_AssetsFairValueDisclosure / gbci_FairValueAssetsAndLiabilitiesByMajorTypesAxis = gbci_OtherRealEstateOwnedMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember |
Other real estate owned | Sales Comparison Approach | Level 3 |  |  |  |
Quantitative Information About Level 3 Fair Value Measurements |  |  |  |
Fair Value | 2,393us-gaap_AssetsFairValueDisclosure / gbci_FairValueAssetsAndLiabilitiesByMajorTypesAxis = gbci_OtherRealEstateOwnedMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember / us-gaap_ValuationTechniqueAxis = gbci_SalesComparisonApproachValuationTechniqueMember |  | 9,278us-gaap_AssetsFairValueDisclosure / gbci_FairValueAssetsAndLiabilitiesByMajorTypesAxis = gbci_OtherRealEstateOwnedMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember / us-gaap_ValuationTechniqueAxis = gbci_SalesComparisonApproachValuationTechniqueMember |
Other real estate owned | Combined Approach | Level 3 |  |  |  |
Quantitative Information About Level 3 Fair Value Measurements |  |  |  |
Fair Value | 607us-gaap_AssetsFairValueDisclosure / gbci_FairValueAssetsAndLiabilitiesByMajorTypesAxis = gbci_OtherRealEstateOwnedMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember / us-gaap_ValuationTechniqueAxis = gbci_CombinedApproachValuationTechniqueMember |  | 1,610us-gaap_AssetsFairValueDisclosure / gbci_FairValueAssetsAndLiabilitiesByMajorTypesAxis = gbci_OtherRealEstateOwnedMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember / us-gaap_ValuationTechniqueAxis = gbci_CombinedApproachValuationTechniqueMember |
Other real estate owned | Minimum Range | Sales Comparison Approach | Level 3 |  |  |  |
Unobservable Inputs |  |  |  |
Selling Costs | 0.00%gbci_FairValueInputsSellingCosts / gbci_FairValueAssetsAndLiabilitiesByMajorTypesAxis = gbci_OtherRealEstateOwnedMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember / us-gaap_RangeAxis = us-gaap_MinimumMember / us-gaap_ValuationTechniqueAxis = gbci_SalesComparisonApproachValuationTechniqueMember | [1] | 7.00%gbci_FairValueInputsSellingCosts / gbci_FairValueAssetsAndLiabilitiesByMajorTypesAxis = gbci_OtherRealEstateOwnedMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember / us-gaap_RangeAxis = us-gaap_MinimumMember / us-gaap_ValuationTechniqueAxis = gbci_SalesComparisonApproachValuationTechniqueMember | [1]
Adjustment to Comparables | 0.00%us-gaap_FairValueInputsComparabilityAdjustments / gbci_FairValueAssetsAndLiabilitiesByMajorTypesAxis = gbci_OtherRealEstateOwnedMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember / us-gaap_RangeAxis = us-gaap_MinimumMember / us-gaap_ValuationTechniqueAxis = gbci_SalesComparisonApproachValuationTechniqueMember | [1] | 0.00%us-gaap_FairValueInputsComparabilityAdjustments / gbci_FairValueAssetsAndLiabilitiesByMajorTypesAxis = gbci_OtherRealEstateOwnedMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember / us-gaap_RangeAxis = us-gaap_MinimumMember / us-gaap_ValuationTechniqueAxis = gbci_SalesComparisonApproachValuationTechniqueMember | [1]
Other real estate owned | Minimum Range | Combined Approach | Level 3 |  |  |  |
Unobservable Inputs |  |  |  |
Selling Costs | 10.00%gbci_FairValueInputsSellingCosts / gbci_FairValueAssetsAndLiabilitiesByMajorTypesAxis = gbci_OtherRealEstateOwnedMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember / us-gaap_RangeAxis = us-gaap_MinimumMember / us-gaap_ValuationTechniqueAxis = gbci_CombinedApproachValuationTechniqueMember | [1] | 5.00%gbci_FairValueInputsSellingCosts / gbci_FairValueAssetsAndLiabilitiesByMajorTypesAxis = gbci_OtherRealEstateOwnedMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember / us-gaap_RangeAxis = us-gaap_MinimumMember / us-gaap_ValuationTechniqueAxis = gbci_CombinedApproachValuationTechniqueMember | [1]
Discount Rate | 10.00%us-gaap_FairValueInputsDiscountRate / gbci_FairValueAssetsAndLiabilitiesByMajorTypesAxis = gbci_OtherRealEstateOwnedMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember / us-gaap_RangeAxis = us-gaap_MinimumMember / us-gaap_ValuationTechniqueAxis = gbci_CombinedApproachValuationTechniqueMember | [1] | 8.50%us-gaap_FairValueInputsDiscountRate / gbci_FairValueAssetsAndLiabilitiesByMajorTypesAxis = gbci_OtherRealEstateOwnedMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember / us-gaap_RangeAxis = us-gaap_MinimumMember / us-gaap_ValuationTechniqueAxis = gbci_CombinedApproachValuationTechniqueMember | [1]
Adjustment to Comparables |  |  | 25.00%us-gaap_FairValueInputsComparabilityAdjustments / gbci_FairValueAssetsAndLiabilitiesByMajorTypesAxis = gbci_OtherRealEstateOwnedMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember / us-gaap_RangeAxis = us-gaap_MinimumMember / us-gaap_ValuationTechniqueAxis = gbci_CombinedApproachValuationTechniqueMember | [1]
Other real estate owned | Maximum Range | Sales Comparison Approach | Level 3 |  |  |  |
Unobservable Inputs |  |  |  |
Selling Costs | 10.00%gbci_FairValueInputsSellingCosts / gbci_FairValueAssetsAndLiabilitiesByMajorTypesAxis = gbci_OtherRealEstateOwnedMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember / us-gaap_RangeAxis = us-gaap_MaximumMember / us-gaap_ValuationTechniqueAxis = gbci_SalesComparisonApproachValuationTechniqueMember | [1] | 10.00%gbci_FairValueInputsSellingCosts / gbci_FairValueAssetsAndLiabilitiesByMajorTypesAxis = gbci_OtherRealEstateOwnedMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember / us-gaap_RangeAxis = us-gaap_MaximumMember / us-gaap_ValuationTechniqueAxis = gbci_SalesComparisonApproachValuationTechniqueMember | [1]
Adjustment to Comparables | 7.00%us-gaap_FairValueInputsComparabilityAdjustments / gbci_FairValueAssetsAndLiabilitiesByMajorTypesAxis = gbci_OtherRealEstateOwnedMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember / us-gaap_RangeAxis = us-gaap_MaximumMember / us-gaap_ValuationTechniqueAxis = gbci_SalesComparisonApproachValuationTechniqueMember | [1] | 37.50%us-gaap_FairValueInputsComparabilityAdjustments / gbci_FairValueAssetsAndLiabilitiesByMajorTypesAxis = gbci_OtherRealEstateOwnedMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember / us-gaap_RangeAxis = us-gaap_MaximumMember / us-gaap_ValuationTechniqueAxis = gbci_SalesComparisonApproachValuationTechniqueMember | [1]
Other real estate owned | Maximum Range | Combined Approach | Level 3 |  |  |  |
Unobservable Inputs |  |  |  |
Selling Costs | 10.00%gbci_FairValueInputsSellingCosts / gbci_FairValueAssetsAndLiabilitiesByMajorTypesAxis = gbci_OtherRealEstateOwnedMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember / us-gaap_RangeAxis = us-gaap_MaximumMember / us-gaap_ValuationTechniqueAxis = gbci_CombinedApproachValuationTechniqueMember | [1] | 10.00%gbci_FairValueInputsSellingCosts / gbci_FairValueAssetsAndLiabilitiesByMajorTypesAxis = gbci_OtherRealEstateOwnedMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember / us-gaap_RangeAxis = us-gaap_MaximumMember / us-gaap_ValuationTechniqueAxis = gbci_CombinedApproachValuationTechniqueMember | [1]
Discount Rate | 10.00%us-gaap_FairValueInputsDiscountRate / gbci_FairValueAssetsAndLiabilitiesByMajorTypesAxis = gbci_OtherRealEstateOwnedMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember / us-gaap_RangeAxis = us-gaap_MaximumMember / us-gaap_ValuationTechniqueAxis = gbci_CombinedApproachValuationTechniqueMember | [1] | 8.50%us-gaap_FairValueInputsDiscountRate / gbci_FairValueAssetsAndLiabilitiesByMajorTypesAxis = gbci_OtherRealEstateOwnedMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember / us-gaap_RangeAxis = us-gaap_MaximumMember / us-gaap_ValuationTechniqueAxis = gbci_CombinedApproachValuationTechniqueMember | [1]
Adjustment to Comparables |  |  | 25.00%us-gaap_FairValueInputsComparabilityAdjustments / gbci_FairValueAssetsAndLiabilitiesByMajorTypesAxis = gbci_OtherRealEstateOwnedMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember / us-gaap_RangeAxis = us-gaap_MaximumMember / us-gaap_ValuationTechniqueAxis = gbci_CombinedApproachValuationTechniqueMember | [1]
Other real estate owned | Weighted Average Range | Sales Comparison Approach | Level 3 |  |  |  |
Unobservable Inputs |  |  |  |
Selling Costs | 5.80%gbci_FairValueInputsSellingCosts / gbci_FairValueAssetsAndLiabilitiesByMajorTypesAxis = gbci_OtherRealEstateOwnedMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember / us-gaap_RangeAxis = us-gaap_WeightedAverageMember / us-gaap_ValuationTechniqueAxis = gbci_SalesComparisonApproachValuationTechniqueMember | [1] | 7.70%gbci_FairValueInputsSellingCosts / gbci_FairValueAssetsAndLiabilitiesByMajorTypesAxis = gbci_OtherRealEstateOwnedMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember / us-gaap_RangeAxis = us-gaap_WeightedAverageMember / us-gaap_ValuationTechniqueAxis = gbci_SalesComparisonApproachValuationTechniqueMember | [1]
Adjustment to Comparables | 0.50%us-gaap_FairValueInputsComparabilityAdjustments / gbci_FairValueAssetsAndLiabilitiesByMajorTypesAxis = gbci_OtherRealEstateOwnedMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember / us-gaap_RangeAxis = us-gaap_WeightedAverageMember / us-gaap_ValuationTechniqueAxis = gbci_SalesComparisonApproachValuationTechniqueMember | [1] | 1.40%us-gaap_FairValueInputsComparabilityAdjustments / gbci_FairValueAssetsAndLiabilitiesByMajorTypesAxis = gbci_OtherRealEstateOwnedMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember / us-gaap_RangeAxis = us-gaap_WeightedAverageMember / us-gaap_ValuationTechniqueAxis = gbci_SalesComparisonApproachValuationTechniqueMember | [1]
Other real estate owned | Weighted Average Range | Combined Approach | Level 3 |  |  |  |
Unobservable Inputs |  |  |  |
Selling Costs | 10.00%gbci_FairValueInputsSellingCosts / gbci_FairValueAssetsAndLiabilitiesByMajorTypesAxis = gbci_OtherRealEstateOwnedMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember / us-gaap_RangeAxis = us-gaap_WeightedAverageMember / us-gaap_ValuationTechniqueAxis = gbci_CombinedApproachValuationTechniqueMember | [1] | 7.50%gbci_FairValueInputsSellingCosts / gbci_FairValueAssetsAndLiabilitiesByMajorTypesAxis = gbci_OtherRealEstateOwnedMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember / us-gaap_RangeAxis = us-gaap_WeightedAverageMember / us-gaap_ValuationTechniqueAxis = gbci_CombinedApproachValuationTechniqueMember | [1]
Discount Rate | 10.00%us-gaap_FairValueInputsDiscountRate / gbci_FairValueAssetsAndLiabilitiesByMajorTypesAxis = gbci_OtherRealEstateOwnedMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember / us-gaap_RangeAxis = us-gaap_WeightedAverageMember / us-gaap_ValuationTechniqueAxis = gbci_CombinedApproachValuationTechniqueMember | [1] | 8.50%us-gaap_FairValueInputsDiscountRate / gbci_FairValueAssetsAndLiabilitiesByMajorTypesAxis = gbci_OtherRealEstateOwnedMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember / us-gaap_RangeAxis = us-gaap_WeightedAverageMember / us-gaap_ValuationTechniqueAxis = gbci_CombinedApproachValuationTechniqueMember | [1]
Adjustment to Comparables |  |  | 25.00%us-gaap_FairValueInputsComparabilityAdjustments / gbci_FairValueAssetsAndLiabilitiesByMajorTypesAxis = gbci_OtherRealEstateOwnedMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember / us-gaap_RangeAxis = us-gaap_WeightedAverageMember / us-gaap_ValuationTechniqueAxis = gbci_CombinedApproachValuationTechniqueMember | [1]
Collateral-dependent Impaired Loans, Net of ALLL | Level 3 |  |  |  |
Quantitative Information About Level 3 Fair Value Measurements |  |  |  |
Fair Value | 15,480us-gaap_AssetsFairValueDisclosure / gbci_FairValueAssetsAndLiabilitiesByMajorTypesAxis = gbci_CollateralDependentImpairedLoansNetOfAlllMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember |  | 18,670us-gaap_AssetsFairValueDisclosure / gbci_FairValueAssetsAndLiabilitiesByMajorTypesAxis = gbci_CollateralDependentImpairedLoansNetOfAlllMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember |
Collateral-dependent Impaired Loans, Net of ALLL | Sales Comparison Approach | Level 3 |  |  |  |
Quantitative Information About Level 3 Fair Value Measurements |  |  |  |
Fair Value | 6,330us-gaap_AssetsFairValueDisclosure / gbci_FairValueAssetsAndLiabilitiesByMajorTypesAxis = gbci_CollateralDependentImpairedLoansNetOfAlllMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember / us-gaap_ValuationTechniqueAxis = gbci_SalesComparisonApproachValuationTechniqueMember |  | 11,784us-gaap_AssetsFairValueDisclosure / gbci_FairValueAssetsAndLiabilitiesByMajorTypesAxis = gbci_CollateralDependentImpairedLoansNetOfAlllMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember / us-gaap_ValuationTechniqueAxis = gbci_SalesComparisonApproachValuationTechniqueMember |
Collateral-dependent Impaired Loans, Net of ALLL | Combined Approach | Level 3 |  |  |  |
Quantitative Information About Level 3 Fair Value Measurements |  |  |  |
Fair Value | 3,809us-gaap_AssetsFairValueDisclosure / gbci_FairValueAssetsAndLiabilitiesByMajorTypesAxis = gbci_CollateralDependentImpairedLoansNetOfAlllMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember / us-gaap_ValuationTechniqueAxis = gbci_CombinedApproachValuationTechniqueMember |  | 2,810us-gaap_AssetsFairValueDisclosure / gbci_FairValueAssetsAndLiabilitiesByMajorTypesAxis = gbci_CollateralDependentImpairedLoansNetOfAlllMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember / us-gaap_ValuationTechniqueAxis = gbci_CombinedApproachValuationTechniqueMember |
Collateral-dependent Impaired Loans, Net of ALLL | Cost Approach | Level 3 |  |  |  |
Quantitative Information About Level 3 Fair Value Measurements |  |  |  |
Fair Value | 6us-gaap_AssetsFairValueDisclosure / gbci_FairValueAssetsAndLiabilitiesByMajorTypesAxis = gbci_CollateralDependentImpairedLoansNetOfAlllMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember / us-gaap_ValuationTechniqueAxis = us-gaap_CostApproachValuationTechniqueMember |  |  |
Collateral-dependent Impaired Loans, Net of ALLL | Income Approach | Level 3 |  |  |  |
Quantitative Information About Level 3 Fair Value Measurements |  |  |  |
Fair Value | 5,335us-gaap_AssetsFairValueDisclosure / gbci_FairValueAssetsAndLiabilitiesByMajorTypesAxis = gbci_CollateralDependentImpairedLoansNetOfAlllMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember / us-gaap_ValuationTechniqueAxis = us-gaap_IncomeApproachValuationTechniqueMember |  | 4,076us-gaap_AssetsFairValueDisclosure / gbci_FairValueAssetsAndLiabilitiesByMajorTypesAxis = gbci_CollateralDependentImpairedLoansNetOfAlllMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember / us-gaap_ValuationTechniqueAxis = us-gaap_IncomeApproachValuationTechniqueMember |
Collateral-dependent Impaired Loans, Net of ALLL | Minimum Range | Sales Comparison Approach | Level 3 |  |  |  |
Unobservable Inputs |  |  |  |
Selling Costs | 0.00%gbci_FairValueInputsSellingCosts / gbci_FairValueAssetsAndLiabilitiesByMajorTypesAxis = gbci_CollateralDependentImpairedLoansNetOfAlllMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember / us-gaap_RangeAxis = us-gaap_MinimumMember / us-gaap_ValuationTechniqueAxis = gbci_SalesComparisonApproachValuationTechniqueMember | [1] | 0.00%gbci_FairValueInputsSellingCosts / gbci_FairValueAssetsAndLiabilitiesByMajorTypesAxis = gbci_CollateralDependentImpairedLoansNetOfAlllMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember / us-gaap_RangeAxis = us-gaap_MinimumMember / us-gaap_ValuationTechniqueAxis = gbci_SalesComparisonApproachValuationTechniqueMember | [1]
Adjustment to Comparables | 0.00%us-gaap_FairValueInputsComparabilityAdjustments / gbci_FairValueAssetsAndLiabilitiesByMajorTypesAxis = gbci_CollateralDependentImpairedLoansNetOfAlllMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember / us-gaap_RangeAxis = us-gaap_MinimumMember / us-gaap_ValuationTechniqueAxis = gbci_SalesComparisonApproachValuationTechniqueMember | [1] | 0.00%us-gaap_FairValueInputsComparabilityAdjustments / gbci_FairValueAssetsAndLiabilitiesByMajorTypesAxis = gbci_CollateralDependentImpairedLoansNetOfAlllMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember / us-gaap_RangeAxis = us-gaap_MinimumMember / us-gaap_ValuationTechniqueAxis = gbci_SalesComparisonApproachValuationTechniqueMember | [1]
Collateral-dependent Impaired Loans, Net of ALLL | Minimum Range | Combined Approach | Level 3 |  |  |  |
Unobservable Inputs |  |  |  |
Selling Costs | 8.00%gbci_FairValueInputsSellingCosts / gbci_FairValueAssetsAndLiabilitiesByMajorTypesAxis = gbci_CollateralDependentImpairedLoansNetOfAlllMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember / us-gaap_RangeAxis = us-gaap_MinimumMember / us-gaap_ValuationTechniqueAxis = gbci_CombinedApproachValuationTechniqueMember | [1] | 0.00%gbci_FairValueInputsSellingCosts / gbci_FairValueAssetsAndLiabilitiesByMajorTypesAxis = gbci_CollateralDependentImpairedLoansNetOfAlllMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember / us-gaap_RangeAxis = us-gaap_MinimumMember / us-gaap_ValuationTechniqueAxis = gbci_CombinedApproachValuationTechniqueMember | [1]
Discount Rate |  |  | 7.30%us-gaap_FairValueInputsDiscountRate / gbci_FairValueAssetsAndLiabilitiesByMajorTypesAxis = gbci_CollateralDependentImpairedLoansNetOfAlllMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember / us-gaap_RangeAxis = us-gaap_MinimumMember / us-gaap_ValuationTechniqueAxis = gbci_CombinedApproachValuationTechniqueMember | [1]
Adjustment to Comparables | 10.00%us-gaap_FairValueInputsComparabilityAdjustments / gbci_FairValueAssetsAndLiabilitiesByMajorTypesAxis = gbci_CollateralDependentImpairedLoansNetOfAlllMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember / us-gaap_RangeAxis = us-gaap_MinimumMember / us-gaap_ValuationTechniqueAxis = gbci_CombinedApproachValuationTechniqueMember | [1] | 10.00%us-gaap_FairValueInputsComparabilityAdjustments / gbci_FairValueAssetsAndLiabilitiesByMajorTypesAxis = gbci_CollateralDependentImpairedLoansNetOfAlllMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember / us-gaap_RangeAxis = us-gaap_MinimumMember / us-gaap_ValuationTechniqueAxis = gbci_CombinedApproachValuationTechniqueMember | [1]
Collateral-dependent Impaired Loans, Net of ALLL | Minimum Range | Cost Approach | Level 3 |  |  |  |
Unobservable Inputs |  |  |  |
Selling Costs | 7.00%gbci_FairValueInputsSellingCosts / gbci_FairValueAssetsAndLiabilitiesByMajorTypesAxis = gbci_CollateralDependentImpairedLoansNetOfAlllMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember / us-gaap_RangeAxis = us-gaap_MinimumMember / us-gaap_ValuationTechniqueAxis = us-gaap_CostApproachValuationTechniqueMember | [1] |  |
Collateral-dependent Impaired Loans, Net of ALLL | Minimum Range | Income Approach | Level 3 |  |  |  |
Unobservable Inputs |  |  |  |
Selling Costs | 8.00%gbci_FairValueInputsSellingCosts / gbci_FairValueAssetsAndLiabilitiesByMajorTypesAxis = gbci_CollateralDependentImpairedLoansNetOfAlllMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember / us-gaap_RangeAxis = us-gaap_MinimumMember / us-gaap_ValuationTechniqueAxis = us-gaap_IncomeApproachValuationTechniqueMember | [1] | 8.00%gbci_FairValueInputsSellingCosts / gbci_FairValueAssetsAndLiabilitiesByMajorTypesAxis = gbci_CollateralDependentImpairedLoansNetOfAlllMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember / us-gaap_RangeAxis = us-gaap_MinimumMember / us-gaap_ValuationTechniqueAxis = us-gaap_IncomeApproachValuationTechniqueMember | [1]
Discount Rate | 8.30%us-gaap_FairValueInputsDiscountRate / gbci_FairValueAssetsAndLiabilitiesByMajorTypesAxis = gbci_CollateralDependentImpairedLoansNetOfAlllMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember / us-gaap_RangeAxis = us-gaap_MinimumMember / us-gaap_ValuationTechniqueAxis = us-gaap_IncomeApproachValuationTechniqueMember | [1] | 8.30%us-gaap_FairValueInputsDiscountRate / gbci_FairValueAssetsAndLiabilitiesByMajorTypesAxis = gbci_CollateralDependentImpairedLoansNetOfAlllMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember / us-gaap_RangeAxis = us-gaap_MinimumMember / us-gaap_ValuationTechniqueAxis = us-gaap_IncomeApproachValuationTechniqueMember | [1]
Collateral-dependent Impaired Loans, Net of ALLL | Maximum Range | Sales Comparison Approach | Level 3 |  |  |  |
Unobservable Inputs |  |  |  |
Selling Costs | 10.00%gbci_FairValueInputsSellingCosts / gbci_FairValueAssetsAndLiabilitiesByMajorTypesAxis = gbci_CollateralDependentImpairedLoansNetOfAlllMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember / us-gaap_RangeAxis = us-gaap_MaximumMember / us-gaap_ValuationTechniqueAxis = gbci_SalesComparisonApproachValuationTechniqueMember | [1] | 10.00%gbci_FairValueInputsSellingCosts / gbci_FairValueAssetsAndLiabilitiesByMajorTypesAxis = gbci_CollateralDependentImpairedLoansNetOfAlllMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember / us-gaap_RangeAxis = us-gaap_MaximumMember / us-gaap_ValuationTechniqueAxis = gbci_SalesComparisonApproachValuationTechniqueMember | [1]
Adjustment to Comparables | 30.00%us-gaap_FairValueInputsComparabilityAdjustments / gbci_FairValueAssetsAndLiabilitiesByMajorTypesAxis = gbci_CollateralDependentImpairedLoansNetOfAlllMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember / us-gaap_RangeAxis = us-gaap_MaximumMember / us-gaap_ValuationTechniqueAxis = gbci_SalesComparisonApproachValuationTechniqueMember | [1] | 1.00%us-gaap_FairValueInputsComparabilityAdjustments / gbci_FairValueAssetsAndLiabilitiesByMajorTypesAxis = gbci_CollateralDependentImpairedLoansNetOfAlllMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember / us-gaap_RangeAxis = us-gaap_MaximumMember / us-gaap_ValuationTechniqueAxis = gbci_SalesComparisonApproachValuationTechniqueMember | [1]
Collateral-dependent Impaired Loans, Net of ALLL | Maximum Range | Combined Approach | Level 3 |  |  |  |
Unobservable Inputs |  |  |  |
Selling Costs | 10.00%gbci_FairValueInputsSellingCosts / gbci_FairValueAssetsAndLiabilitiesByMajorTypesAxis = gbci_CollateralDependentImpairedLoansNetOfAlllMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember / us-gaap_RangeAxis = us-gaap_MaximumMember / us-gaap_ValuationTechniqueAxis = gbci_CombinedApproachValuationTechniqueMember | [1] | 8.00%gbci_FairValueInputsSellingCosts / gbci_FairValueAssetsAndLiabilitiesByMajorTypesAxis = gbci_CollateralDependentImpairedLoansNetOfAlllMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember / us-gaap_RangeAxis = us-gaap_MaximumMember / us-gaap_ValuationTechniqueAxis = gbci_CombinedApproachValuationTechniqueMember | [1]
Discount Rate |  |  | 7.30%us-gaap_FairValueInputsDiscountRate / gbci_FairValueAssetsAndLiabilitiesByMajorTypesAxis = gbci_CollateralDependentImpairedLoansNetOfAlllMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember / us-gaap_RangeAxis = us-gaap_MaximumMember / us-gaap_ValuationTechniqueAxis = gbci_CombinedApproachValuationTechniqueMember | [1]
Adjustment to Comparables | 20.00%us-gaap_FairValueInputsComparabilityAdjustments / gbci_FairValueAssetsAndLiabilitiesByMajorTypesAxis = gbci_CollateralDependentImpairedLoansNetOfAlllMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember / us-gaap_RangeAxis = us-gaap_MaximumMember / us-gaap_ValuationTechniqueAxis = gbci_CombinedApproachValuationTechniqueMember | [1] | 50.00%us-gaap_FairValueInputsComparabilityAdjustments / gbci_FairValueAssetsAndLiabilitiesByMajorTypesAxis = gbci_CollateralDependentImpairedLoansNetOfAlllMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember / us-gaap_RangeAxis = us-gaap_MaximumMember / us-gaap_ValuationTechniqueAxis = gbci_CombinedApproachValuationTechniqueMember | [1]
Collateral-dependent Impaired Loans, Net of ALLL | Maximum Range | Cost Approach | Level 3 |  |  |  |
Unobservable Inputs |  |  |  |
Selling Costs | 7.00%gbci_FairValueInputsSellingCosts / gbci_FairValueAssetsAndLiabilitiesByMajorTypesAxis = gbci_CollateralDependentImpairedLoansNetOfAlllMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember / us-gaap_RangeAxis = us-gaap_MaximumMember / us-gaap_ValuationTechniqueAxis = us-gaap_CostApproachValuationTechniqueMember | [1] |  |
Collateral-dependent Impaired Loans, Net of ALLL | Maximum Range | Income Approach | Level 3 |  |  |  |
Unobservable Inputs |  |  |  |
Selling Costs | 10.00%gbci_FairValueInputsSellingCosts / gbci_FairValueAssetsAndLiabilitiesByMajorTypesAxis = gbci_CollateralDependentImpairedLoansNetOfAlllMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember / us-gaap_RangeAxis = us-gaap_MaximumMember / us-gaap_ValuationTechniqueAxis = us-gaap_IncomeApproachValuationTechniqueMember | [1] | 8.00%gbci_FairValueInputsSellingCosts / gbci_FairValueAssetsAndLiabilitiesByMajorTypesAxis = gbci_CollateralDependentImpairedLoansNetOfAlllMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember / us-gaap_RangeAxis = us-gaap_MaximumMember / us-gaap_ValuationTechniqueAxis = us-gaap_IncomeApproachValuationTechniqueMember | [1]
Discount Rate | 12.00%us-gaap_FairValueInputsDiscountRate / gbci_FairValueAssetsAndLiabilitiesByMajorTypesAxis = gbci_CollateralDependentImpairedLoansNetOfAlllMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember / us-gaap_RangeAxis = us-gaap_MaximumMember / us-gaap_ValuationTechniqueAxis = us-gaap_IncomeApproachValuationTechniqueMember | [1] | 8.30%us-gaap_FairValueInputsDiscountRate / gbci_FairValueAssetsAndLiabilitiesByMajorTypesAxis = gbci_CollateralDependentImpairedLoansNetOfAlllMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember / us-gaap_RangeAxis = us-gaap_MaximumMember / us-gaap_ValuationTechniqueAxis = us-gaap_IncomeApproachValuationTechniqueMember | [1]
Collateral-dependent Impaired Loans, Net of ALLL | Weighted Average Range | Sales Comparison Approach | Level 3 |  |  |  |
Unobservable Inputs |  |  |  |
Selling Costs | 8.30%gbci_FairValueInputsSellingCosts / gbci_FairValueAssetsAndLiabilitiesByMajorTypesAxis = gbci_CollateralDependentImpairedLoansNetOfAlllMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember / us-gaap_RangeAxis = us-gaap_WeightedAverageMember / us-gaap_ValuationTechniqueAxis = gbci_SalesComparisonApproachValuationTechniqueMember | [1] | 7.90%gbci_FairValueInputsSellingCosts / gbci_FairValueAssetsAndLiabilitiesByMajorTypesAxis = gbci_CollateralDependentImpairedLoansNetOfAlllMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember / us-gaap_RangeAxis = us-gaap_WeightedAverageMember / us-gaap_ValuationTechniqueAxis = gbci_SalesComparisonApproachValuationTechniqueMember | [1]
Adjustment to Comparables | 3.50%us-gaap_FairValueInputsComparabilityAdjustments / gbci_FairValueAssetsAndLiabilitiesByMajorTypesAxis = gbci_CollateralDependentImpairedLoansNetOfAlllMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember / us-gaap_RangeAxis = us-gaap_WeightedAverageMember / us-gaap_ValuationTechniqueAxis = gbci_SalesComparisonApproachValuationTechniqueMember | [1] | 0.00%us-gaap_FairValueInputsComparabilityAdjustments / gbci_FairValueAssetsAndLiabilitiesByMajorTypesAxis = gbci_CollateralDependentImpairedLoansNetOfAlllMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember / us-gaap_RangeAxis = us-gaap_WeightedAverageMember / us-gaap_ValuationTechniqueAxis = gbci_SalesComparisonApproachValuationTechniqueMember | [1]
Collateral-dependent Impaired Loans, Net of ALLL | Weighted Average Range | Combined Approach | Level 3 |  |  |  |
Unobservable Inputs |  |  |  |
Selling Costs | 9.20%gbci_FairValueInputsSellingCosts / gbci_FairValueAssetsAndLiabilitiesByMajorTypesAxis = gbci_CollateralDependentImpairedLoansNetOfAlllMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember / us-gaap_RangeAxis = us-gaap_WeightedAverageMember / us-gaap_ValuationTechniqueAxis = gbci_CombinedApproachValuationTechniqueMember | [1] | 7.80%gbci_FairValueInputsSellingCosts / gbci_FairValueAssetsAndLiabilitiesByMajorTypesAxis = gbci_CollateralDependentImpairedLoansNetOfAlllMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember / us-gaap_RangeAxis = us-gaap_WeightedAverageMember / us-gaap_ValuationTechniqueAxis = gbci_CombinedApproachValuationTechniqueMember | [1]
Discount Rate |  |  | 7.30%us-gaap_FairValueInputsDiscountRate / gbci_FairValueAssetsAndLiabilitiesByMajorTypesAxis = gbci_CollateralDependentImpairedLoansNetOfAlllMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember / us-gaap_RangeAxis = us-gaap_WeightedAverageMember / us-gaap_ValuationTechniqueAxis = gbci_CombinedApproachValuationTechniqueMember | [1]
Adjustment to Comparables | 16.20%us-gaap_FairValueInputsComparabilityAdjustments / gbci_FairValueAssetsAndLiabilitiesByMajorTypesAxis = gbci_CollateralDependentImpairedLoansNetOfAlllMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember / us-gaap_RangeAxis = us-gaap_WeightedAverageMember / us-gaap_ValuationTechniqueAxis = gbci_CombinedApproachValuationTechniqueMember | [1] | 18.90%us-gaap_FairValueInputsComparabilityAdjustments / gbci_FairValueAssetsAndLiabilitiesByMajorTypesAxis = gbci_CollateralDependentImpairedLoansNetOfAlllMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember / us-gaap_RangeAxis = us-gaap_WeightedAverageMember / us-gaap_ValuationTechniqueAxis = gbci_CombinedApproachValuationTechniqueMember | [1]
Collateral-dependent Impaired Loans, Net of ALLL | Weighted Average Range | Cost Approach | Level 3 |  |  |  |
Unobservable Inputs |  |  |  |
Selling Costs | 7.00%gbci_FairValueInputsSellingCosts / gbci_FairValueAssetsAndLiabilitiesByMajorTypesAxis = gbci_CollateralDependentImpairedLoansNetOfAlllMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember / us-gaap_RangeAxis = us-gaap_WeightedAverageMember / us-gaap_ValuationTechniqueAxis = us-gaap_CostApproachValuationTechniqueMember | [1] |  |
Collateral-dependent Impaired Loans, Net of ALLL | Weighted Average Range | Income Approach | Level 3 |  |  |  |
Unobservable Inputs |  |  |  |
Selling Costs | 8.50%gbci_FairValueInputsSellingCosts / gbci_FairValueAssetsAndLiabilitiesByMajorTypesAxis = gbci_CollateralDependentImpairedLoansNetOfAlllMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember / us-gaap_RangeAxis = us-gaap_WeightedAverageMember / us-gaap_ValuationTechniqueAxis = us-gaap_IncomeApproachValuationTechniqueMember | [1] | 8.00%gbci_FairValueInputsSellingCosts / gbci_FairValueAssetsAndLiabilitiesByMajorTypesAxis = gbci_CollateralDependentImpairedLoansNetOfAlllMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember / us-gaap_RangeAxis = us-gaap_WeightedAverageMember / us-gaap_ValuationTechniqueAxis = us-gaap_IncomeApproachValuationTechniqueMember | [1]
Discount Rate | 9.10%us-gaap_FairValueInputsDiscountRate / gbci_FairValueAssetsAndLiabilitiesByMajorTypesAxis = gbci_CollateralDependentImpairedLoansNetOfAlllMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember / us-gaap_RangeAxis = us-gaap_WeightedAverageMember / us-gaap_ValuationTechniqueAxis = us-gaap_IncomeApproachValuationTechniqueMember | [1] | 8.30%us-gaap_FairValueInputsDiscountRate / gbci_FairValueAssetsAndLiabilitiesByMajorTypesAxis = gbci_CollateralDependentImpairedLoansNetOfAlllMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember / us-gaap_RangeAxis = us-gaap_WeightedAverageMember / us-gaap_ValuationTechniqueAxis = us-gaap_IncomeApproachValuationTechniqueMember | [1]
[1] | The range for selling costs and adjustments to comparables indicate reductions to the fair value.

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