Name:	gbnk_AvailableForSaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositionsForTwelveMonthsOrLonger
Namespace Prefix:	gbnk_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	instant

Represents the book value of single issuer security.

No definition available.

Name:	gbnk_BookValueOfSingleIssuerSecurity
Namespace Prefix:	gbnk_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

A prepayment of future principal payments on an investment held by the Company.

No definition available.

Name:	gbnk_EarlyRedmptionOfSeniorDebt
Namespace Prefix:	gbnk_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Percent Of Unrated Municipal Bond Securities

No definition available.

Name:	gbnk_PercentOfUnratedMunicipalBondSecurities
Namespace Prefix:	gbnk_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

Security Of Single Issuers Percent Of Stockholders Equity

No definition available.

Name:	gbnk_SecurityOfSingleIssuersPercentOfStockholdersEquity
Namespace Prefix:	gbnk_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

Amount of the excess of amortized cost basis over fair value of securities in a loss position and categorized neither as held-to-maturity nor trading securities.

Name:	us-gaap_AvailableforsaleSecuritiesContinuousUnrealizedLossPositionAggregateLosses2
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Disclosure regarding factors used to determine that the impairment of securities not categorized as either held-to-maturity securities or trading securities (hence equal to available for sale securities) where cost exceeds fair value is not an other than temporary impairment (OTTI). This item contains disclosure of the number of investment positions in the available-for-sale investments determined to be temporarily impaired.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 6

-Subparagraph (b)(3)

-URI http://asc.fasb.org/extlink&oid=6872113&loc=d3e27290-111563

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Emerging Issues Task Force (EITF)

-Number 03-1

-Paragraph 21

-Subparagraph b(3)

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name FASB Staff Position (FSP)

-Number FAS115-1/124-1

-Paragraph 17

-Subparagraph b(3)

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Name:	us-gaap_AvailableForSaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositions
Namespace Prefix:	us-gaap_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	instant

Interest rate stated in the contractual debt agreement.

Name:	us-gaap_DebtInstrumentInterestRateStatedPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

Date when the debt instrument is scheduled to be fully repaid, in CCYY-MM-DD format.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 22

-Article 5

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.22(a)(2))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 129

-Paragraph 2, 4

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.