Deposits - Narrative (Details) - USD ($)	Dec. 31, 2024	Dec. 31, 2023
Deposits
FDIC Insurance limit	$ 250,000	$ 250,000
Time deposits that meet or exceed FDIC Insurance limit	1,089,163,000	1,227,607,000
Whole sale deposits	0
Overdraft demand deposits reclassified as loans	11,694,000	8,242,000
Deposits with related parties	$ 30,403,000	$ 31,706,000

Deposits textual.

No definition available.

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- 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
-Topic 942
-SubTopic 210
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(12))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478546/942-210-S99-1

+ 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
-Topic 235
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(k)(1))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480678/235-10-S99-1

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant