Loans and Allowance - Allowance by Loan Segment (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance, beginning of year	$ 1,476	$ 2,066	$ 2,066
Impact of ASC 326 adoption	1,574
Charged off	(81)	(125)	(392)
Recoveries	356		491
Provision for loan losses	(404)	(80)	689
Balance, end of year	2,921		1,476
Individually evaluated for impairment:
Individually evaluated for impairment, Balance in allowance	11		11
Individually evaluated for impairment, Related loan balance	38		4,664
Collectively evaluated for impairment:
Collectively evaluated for impairment, Balance in allowance	2,910		1,465
Collectively evaluated for impairment, Related loan balance	246,815		249,108
Real Estate Loan
Individually evaluated for impairment:
Individually evaluated for impairment, Balance in allowance	11		11
Construction And Land Development \| Real Estate Loan
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance, beginning of year	9	24	24
Impact of ASC 326 adoption	16
Provision for loan losses	7		15
Balance, end of year	32		9
Collectively evaluated for impairment:
Collectively evaluated for impairment, Balance in allowance	32		9
Collectively evaluated for impairment, Related loan balance	3,174		2,553
Farmland \| Real Estate Loan
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance, beginning of year	2	2	2
Impact of ASC 326 adoption	9
Provision for loan losses	(1)
Balance, end of year	10		2
Collectively evaluated for impairment:
Collectively evaluated for impairment, Balance in allowance	10		2
Collectively evaluated for impairment, Related loan balance	349		350
Single-family residential \| Real Estate Loan
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance, beginning of year	513	849	849
Impact of ASC 326 adoption	854
Recoveries	275		266
Provision for loan losses	(272)		602
Balance, end of year	1,370		513
Individually evaluated for impairment:
Individually evaluated for impairment, Balance in allowance	11		11
Individually evaluated for impairment, Related loan balance	38		132
Collectively evaluated for impairment:
Collectively evaluated for impairment, Balance in allowance	1,359		513
Collectively evaluated for impairment, Related loan balance	82,782		82,388
Multifamily \| Real Estate Loan
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance, beginning of year	39	40	40
Impact of ASC 326 adoption	63
Provision for loan losses			1
Balance, end of year	102		39
Collectively evaluated for impairment:
Collectively evaluated for impairment, Balance in allowance	102		39
Collectively evaluated for impairment, Related loan balance	6,069		6,105
Commercial And Industrial Portfolio Segment [Member] \| Commercial and Industrial Sector [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance, beginning of year	67	69	69
Impact of ASC 326 adoption	120
Recoveries			20
Provision for loan losses	(19)		22
Balance, end of year	168		67
Individually evaluated for impairment:
Individually evaluated for impairment, Related loan balance			4,493
Collectively evaluated for impairment:
Collectively evaluated for impairment, Balance in allowance	168		67
Collectively evaluated for impairment, Related loan balance	9,521		6,307
Commercial \| Real Estate Loan
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance, beginning of year	218	241	241
Impact of ASC 326 adoption	199
Provision for loan losses	(8)		23
Balance, end of year	409		218
Collectively evaluated for impairment:
Collectively evaluated for impairment, Balance in allowance	409		218
Collectively evaluated for impairment, Related loan balance	55,723		57,027
SBA Guaranty \| Commercial and Industrial Sector [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance, beginning of year	48	25	25
Impact of ASC 326 adoption	(6)
Provision for loan losses	(1)		(23)
Balance, end of year	41		48
Collectively evaluated for impairment:
Collectively evaluated for impairment, Balance in allowance	41		48
Collectively evaluated for impairment, Related loan balance	7,192		7,200
Comm SBA PPP \| Commercial and Industrial Sector [Member]
Collectively evaluated for impairment:
Collectively evaluated for impairment, Related loan balance	11,244		9,912
Consumer \| Consumer Loan [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance, beginning of year	11	11	11
Impact of ASC 326 adoption	46
Recoveries			6
Provision for loan losses	(11)		6
Balance, end of year	46		11
Individually evaluated for impairment:
Individually evaluated for impairment, Balance in allowance			11
Individually evaluated for impairment, Related loan balance			39
Collectively evaluated for impairment:
Collectively evaluated for impairment, Balance in allowance	46
Collectively evaluated for impairment, Related loan balance	2,482		3,024
Automobile \| Consumer Loan [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance, beginning of year	569	$ 805	805
Impact of ASC 326 adoption	273
Charged off	(81)		(392)
Recoveries	81		199
Provision for loan losses	(99)		43
Balance, end of year	743		569
Collectively evaluated for impairment:
Collectively evaluated for impairment, Balance in allowance	743		569
Collectively evaluated for impairment, Related loan balance	$ 68,279		$ 74,242

No definition available.

Name:	glbz_CollectivelyEvaluatedForImpairmentAbstract
Namespace Prefix:	glbz_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of adjustment from adoption of ASC to financing receivable, charged against allowance for credit loss.

+ References

No definition available.

+ Details

Name:	glbz_FinancingReceivableAllowanceForCreditLossesImpactOfAdoption
Namespace Prefix:	glbz_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- References

No definition available.

+ Details

Name:	glbz_IndividuallyEvaluatedForImpairmentAbstract
Namespace Prefix:	glbz_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of allowance for credit loss on financing receivable. Excludes allowance for financing receivable covered under loss sharing agreement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=121611835&loc=SL6953423-111524

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(7)(2))
-URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=121599878&loc=SL82895884-210446

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 13
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=121599337&loc=SL82919249-210447

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 13
-Subparagraph (f)
-URI http://asc.fasb.org/extlink&oid=121599337&loc=SL82919249-210447

+ Details

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

- Definition

The valuation allowance for financing receivables that are expected to be uncollectible that were collectively evaluated for impairment.

+ References

+ Details

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

- Definition

Amount of valuation allowance for financing receivables that are expected to be uncollectible that were individually evaluated for impairment.

+ References

+ Details

Name:	us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of increase in allowance for credit loss on financing receivable from recovery.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 55
-Paragraph 79
-URI http://asc.fasb.org/extlink&oid=121647567&loc=SL82922352-210448

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 13
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=121599337&loc=SL82919249-210447

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (c)(4)
-URI http://asc.fasb.org/extlink&oid=121611835&loc=SL6953423-111524

+ Details

Name:	us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

+ Details

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

- Definition

Amount of writeoff of financing receivable, charged against allowance for credit loss.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 13
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=121599337&loc=SL82919249-210447

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (c)(3)
-URI http://asc.fasb.org/extlink&oid=121611835&loc=SL6953423-111524

Reference 3: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 55
-Paragraph 79
-URI http://asc.fasb.org/extlink&oid=121647567&loc=SL82922352-210448

+ Details

Name:	us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The balance of financing receivables that were collectively evaluated for impairment.

+ References

+ Details

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

- Definition

The balance of financing receivables that were individually evaluated for impairment.

+ References

+ Details

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

- Definition

Amount of expense related loan transactions, lease transactions, credit loss from transactions other than loan and lease transactions, and other loss based on assessment of uncollectability from the counterparty to reduce the account to their net realizable value.

+ References

+ Details

Name:	us-gaap_ProvisionForLoanLeaseAndOtherLosses
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_RealEstateLoanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=glbz_ConstructionAndLandDevelopmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=glbz_FarmlandMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=srt_SingleFamilyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=srt_MultifamilyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=glbz_CommercialAndIndustrialPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_CommercialAndIndustrialSectorMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_CommercialPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=glbz_SbaGuarantyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=glbz_CommSbaPppMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_ConsumerPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_ConsumerLoanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_AutomobileLoanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: