Deposits - Narrative (Details) - USD ($)	Dec. 31, 2022	Dec. 31, 2021
Deposits
FDIC Insurance limit	$ 250,000
Time deposits that meet or exceed FDIC Insurance limit	243,219,000	$ 298,512,000
Whole sale deposits	28,489,000
Overdraft demand deposits reclassified as loans	8,737,000	10,036,000
Deposits with related parties	$ 37,046,000	$ 55,966,000

Deposits textual.

No definition available.

Name:	gbci_DepositsTextualAbstract
Namespace Prefix:	gbci_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Overdraft demand deposits reclassified as loans.

+ References

No definition available.

+ Details

Name:	gbci_OverdraftDemandDepositsReclassifiedAsLoans
Namespace Prefix:	gbci_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The aggregate amount of domestic time deposit liabilities (including certificates of deposits, individual retirement accounts and open accounts) in denominations that meet or exceed the FDIC Insurance limit.

+ References

No definition available.

+ Details

Name:	gbci_TimeDepositsThatMeetOrExceedFDICInsuranceLimit
Namespace Prefix:	gbci_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The amount of cash deposited in financial institutions as of the balance sheet date that is insured by the Federal Deposit Insurance Corporation.

+ References

No definition available.

+ Details

Name:	us-gaap_CashFDICInsuredAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The aggregate amount of all wholesale deposit accounts including certificates of deposits.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.12)
-URI https://asc.fasb.org/extlink&oid=126897435&loc=d3e534808-122878

+ Details

Name:	us-gaap_DepositsWholesale
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of deposits held by the entity for a related party (entity, shareholder, employee).

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(k)(1))
-URI https://asc.fasb.org/extlink&oid=120395691&loc=d3e23780-122690

+ Details

Name:	us-gaap_RelatedPartyDepositLiabilities
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant