Variable Interest Entities VIE Carrying Amounts Included in Financial Statements (Details) - Consolidated VIEs - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Consolidated VIEs
Assets	$ 50,625	$ 72,175
Liabilities	4,606	6,343
Loans Receivable
Consolidated VIEs
Assets	49,260	57,126
Premises and Equipment, Net
Consolidated VIEs
Assets	0	13,503
Accrued Interest Receivable
Consolidated VIEs
Assets	167	117
Other assets
Consolidated VIEs
Assets	1,198	1,429
Other borrowed funds
Consolidated VIEs
Liabilities	4,555	6,195
Accrued interest payable
Consolidated VIEs
Liabilities	4	9
Other liabilities
Consolidated VIEs
Liabilities	$ 47	$ 139

The carrying amount of the consolidated Variable Interest Entity's assets included in the reporting entity's statement of financial position.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (bb)
-URI http://asc.fasb.org/extlink&oid=64801991&loc=d3e5710-111685

+ Details

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

- Definition

The carrying amount of the consolidated Variable Interest Entity's liabilities included in the reporting entity's statement of financial position.

+ References

+ Details

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

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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

- Details

Name:	us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis=us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BalanceSheetLocationAxis=us-gaap_LoansReceivableMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BalanceSheetLocationAxis=us-gaap_PropertyPlantAndEquipmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BalanceSheetLocationAxis=gbci_AccruedInterestReceivableMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BalanceSheetLocationAxis=us-gaap_PrepaidExpensesAndOtherCurrentAssetsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BalanceSheetLocationAxis=us-gaap_BorrowingsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BalanceSheetLocationAxis=gbci_AccruedInterestPayableMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BalanceSheetLocationAxis=us-gaap_AccountsPayableAndAccruedLiabilitiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: