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v2.4.1.9

Premises and Equipment (Details Textual) (USD $) | 12 Months Ended
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Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012
Premises and Equipment |  |  |
Depreciation expense | $ 12,108,000us-gaap_DepreciationNonproduction | $ 10,485,000us-gaap_DepreciationNonproduction | $ 10,615,000us-gaap_DepreciationNonproduction
Total rent expense | 2,786,000us-gaap_LeaseAndRentalExpense | 2,912,000us-gaap_LeaseAndRentalExpense | 2,868,000us-gaap_LeaseAndRentalExpense
Related party rent expense | $ 146,000gbci_RelatedPartyRentExpense | $ 142,000gbci_RelatedPartyRentExpense | $ 410,000gbci_RelatedPartyRentExpense

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- Details
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Namespace Prefix: | gbci_
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Balance Type: | na
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- Definition Related party rent expense. + References No definition available. + Details
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Namespace Prefix: | gbci_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition The expense recognized in the current period that allocates the cost of nonproduction tangible assets over their useful lives. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 360 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=6391035&loc=d3e2868-110229 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585 + Details
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Balance Type: | debit
Period Type: | duration

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- Definition Amount of rent expense incurred for leased assets, including but not limited to, furniture and equipment, that is not directly or indirectly associated with the manufacture, sale or creation of a product or product line. + References No definition available. + Details
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Namespace Prefix: | us-gaap_
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Balance Type: | debit
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