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v2.4.1.9

Investment Securities (Details Textual) (USD $) | 12 Months Ended |
--- | --- | ---
Dec. 31, 2014 | Dec. 31, 2013 | Jan. 01, 2014
Investment Securities |  |  |
Investment securities pledged as collateral | $ 1,673,263,000us-gaap_SecurityOwnedAndPledgedAsCollateralFairValue | $ 1,635,316,000us-gaap_SecurityOwnedAndPledgedAsCollateralFairValue |
Other-than-temporary impairment on investment securities | 0us-gaap_ImpairmentOfInvestments | 0us-gaap_ImpairmentOfInvestments |
State and local governments |  |  |
Investment Securities |  |  |
Available-for-sale Securities, Transferred to Held-to-Maturity Securities, Fair Value |  |  | 484,583,000gbci_AvailableforsaleSecuritiesTransferredtoHeldtoMaturitySecuritiesFairValue / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember
Available-for-sale Securities, Transferred to Held-to-Maturity Securities, Unrealized Gain (Loss) |  |  | $ 4,624,000gbci_AvailableforsaleSecuritiesTransferredtoHeldtoMaturitySecuritiesUnrealizedGainLoss / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember

X
- Definition For any transfer of securities categorized as available-for-sale, this item represents the estimated fair value of the transferred security to held-to-maturity securities. + References No definition available. + Details
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Namespace Prefix: | gbci_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition This item represents the unrealized gain (loss) recognized in other comprehensive income (a separate component of shareholders' equity) prior to the available-for-sale securities being transferred to the held-to-maturity category. + References No definition available. + Details
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- Details
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- Definition The amount by which the fair value of an investment is less than the amortized cost basis or carrying amount of that investment at the balance sheet date and the decline in fair value is deemed to be other than temporary, before considering whether or not such amount is recognized in earnings or other comprehensive income. + References Reference 1: 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 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 35 -Paragraph 34 -URI http://asc.fasb.org/extlink&oid=27723805&loc=d3e25351-111560 + Details
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Balance Type: | debit
Period Type: | duration

X
- Definition Fair value of financial instrument held by the entity for its own account (proprietary securities) for trading or investment purposes that are carried at fair value and pledged to counterparties as collateral for financing transactions. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 860 -SubTopic 30 -Section 50 -Paragraph 1A -Subparagraph (b)(1)(i) -URI http://asc.fasb.org/extlink&oid=34720971&loc=SL6224234-111729 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 860 -SubTopic 30 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6467456&loc=d3e113888-111728 + Details
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- Details
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