XML 102 R90.htm IDEA: XBRL DOCUMENT
v3.20.4

Subordinated Debentures - Narrative (Details) | 12 Months Ended
--- | ---
Dec. 31, 2020 USD ($)
Debt Instruments [Abstract] |
Maximum number of consecutive quarters for deferral of interest payments on trust preferred securities | 20
Size of company eligible for Tier 1 grandfather provision | $ 15,000,000,000
Number of years before allowed to prepay Tier 2 subordinated debt | 5

X
- Definition Maximum Number Of Consecutive Quarters For Deferral Of Interest Payments On Trust Preferred Securities + References No definition available. + Details
Name: | gbci_MaximumNumberOfConsecutiveQuartersForDeferralOfInterestPaymentsOnTrustPreferredSecurities
Namespace Prefix: | gbci_
Data Type: | us-types:durationStringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Number Of Years Before Allowed To Prepay Debt + References No definition available. + Details
Name: | gbci_NumberOfYearsBeforeAllowedToPrepayDebt
Namespace Prefix: | gbci_
Data Type: | us-types:durationStringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Size of company eligible for Tier 1 grandfather provision. + References No definition available. + Details
Name: | gbci_SizeOfCompanyEligibleForTier1GrandfatherProvision
Namespace Prefix: | gbci_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- References No definition available. + Details
Name: | us-gaap_DebtInstrumentsAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration