Carrying amount as of the balance sheet date of interest earned but not received on financing receivable.

No definition available.

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- Definition

Amount of premiums over or discounts from face amounts of loans that are being amortized into income as an adjustment to yield.

+ References

No definition available.

+ Details

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Balance Type:	debit
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- Definition

Amount of deferred fees paid by borrowers and unamortized costs incurred to originate loans and leases.

+ References

No definition available.

+ Details

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Namespace Prefix:	gbci_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount excluding accrued interest, of allowance for credit loss on financing receivable.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=124255206&loc=SL82895884-210446

+ Details

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

- Definition

Amount excluding accrued interest, after allowance for credit loss, of financing receivable.

+ References

+ Details

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

- Definition

Amount excluding accrued interest, before allowance for credit loss, of financing receivable.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 5
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=124255953&loc=SL82919230-210447

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=124255206&loc=SL82895884-210446

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 3B
-URI http://asc.fasb.org/extlink&oid=124255953&loc=SL120267963-210447

+ Details

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

- References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_ResidentialPortfolioSegmentMember
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- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_CommercialRealEstatePortfolioSegmentMember
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- Details

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- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=gbci_HomeEquityPortfolioSegmentMember
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- Details

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Loans Receivable, Net - Summary of Loans Receivable (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Jun. 30, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Dec. 31, 2019
Summary of Loans Receivable
Loans receivable	$ 11,293,891		$ 11,122,696
Allowance for credit losses	(153,609)	$ (151,448)	(158,243)	$ (164,552)	$ (162,509)	$ (124,490)
Loans receivable, net	11,140,282		10,964,453
Net deferred origination (fees) costs included in loans receivable	(26,325)		(26,709)
Net purchase accounting (discounts) premiums included in loans receivable	(12,458)		(17,091)
Accrued interest receivable on loans	50,229		53,538
Residential real estate
Summary of Loans Receivable
Loans receivable	781,538		802,508
Allowance for credit losses	(11,859)	(10,143)	(9,604)	(9,805)	(9,986)	(10,111)
Commercial real estate
Summary of Loans Receivable
Loans receivable	6,912,569		6,315,895
Allowance for credit losses	(100,038)	(96,597)	(86,999)	(94,397)	(89,104)	(69,496)
Other commercial
Summary of Loans Receivable
Loans receivable	2,598,616		3,054,817
Allowance for credit losses	(28,845)	(31,983)	(49,133)	(48,753)	(48,838)	(36,129)
Home equity
Summary of Loans Receivable
Loans receivable	660,920		636,405
Allowance for credit losses	(7,865)	(7,837)	(8,182)	(7,430)	(9,962)	(4,937)
Other consumer
Summary of Loans Receivable
Loans receivable	340,248		313,071
Allowance for credit losses	$ (5,002)	$ (4,888)	$ (4,325)	$ (4,167)	$ (4,619)	$ (3,817)