LOANS AND ALLOWANCE FOR CREDIT LOSSES - Schedule of Allowance for Credit Losses Activity (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023
Allowance for credit losses:
Beginning balance	$ 30,920	$ 31,974	$ 31,974
Provision for (reversal of) credit losses	(250)	0	0
Loans charged-off	(310)	(94)	(1,204)
Recoveries	200	73	150
Ending balance	30,560	31,953	30,920
Commercial and industrial
Allowance for credit losses:
Beginning balance	3,719	4,382	4,382
Provision for (reversal of) credit losses	67	(239)	(209)
Loans charged-off	(216)	(3)	(473)
Recoveries	174	8	19
Ending balance	3,744	4,148	3,719
Construction and development
Allowance for credit losses:
Beginning balance	3,623	4,889	4,889
Provision for (reversal of) credit losses	(363)	(25)	(1,266)
Loans charged-off		0	0
Recoveries	0	0	0
Ending balance	3,260	4,864	3,623
Commercial real estate
Allowance for credit losses:
Beginning balance	12,257	12,658	12,658
Provision for (reversal of) credit losses	19	32	(124)
Loans charged-off	0	0	(277)
Recoveries	0	0	0
Ending balance	12,276	12,690	12,257
Farmland
Allowance for credit losses:
Beginning balance	2,231	2,008	2,008
Provision for (reversal of) credit losses	(27)	78	223
Loans charged-off		0	0
Ending balance	2,204	2,086	2,231
1-4 family residential
Allowance for credit losses:
Beginning balance	7,470	6,617	6,617
Provision for (reversal of) credit losses	215	24	853
Loans charged-off		0	0
Recoveries	0	0	0
Ending balance	7,685	6,641	7,470
Multi-family residential
Allowance for credit losses:
Beginning balance	521	490	490
Provision for (reversal of) credit losses	(4)	(11)	31
Loans charged-off		0	0
Ending balance	517	479	521
Consumer
Allowance for credit losses:
Beginning balance	945	778	778
Provision for (reversal of) credit losses	(194)	82	238
Loans charged-off	(35)	(7)	(139)
Recoveries	7	45	68
Ending balance	723	898	945
Agricultural
Allowance for credit losses:
Beginning balance	152	149	149
Provision for (reversal of) credit losses	(6)	(4)	4
Loans charged-off	0	(3)	(3)
Recoveries	2	2	2
Ending balance	148	144	152
Overdrafts
Allowance for credit losses:
Beginning balance	2	3	3
Provision for (reversal of) credit losses	43	63	250
Loans charged-off	(59)	(81)	(312)
Recoveries	17	18	61
Ending balance	$ 3	$ 3	$ 2

Provision for loan losses and credit losses.

No definition available.

Name:	gnty_ProvisionForLoanLossesAndCreditLosses
Namespace Prefix:	gnty_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of recovery of loans and lease receivables which had previously been fully or partially written-off as bad debts.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section 50
-Paragraph 11B
-Subparagraph (c)(4)
-SubTopic 10
-Topic 310
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481962/310-10-50-11B

+ Details

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

- Definition

Amount of loans and leases that have been written off from both loan receivables and allowance reserve for credit loss.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section 50
-Paragraph 11B
-Subparagraph (c)(3)
-SubTopic 10
-Topic 310
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481962/310-10-50-11B

+ Details

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

- Definition

Amount of allowance to cover probable credit losses on loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations. Excludes allowance for loans and leases covered under loss sharing agreements.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 310
-SubTopic 30
-Section 50
-Paragraph 2
-Subparagraph (b)(1)(ii)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481696/310-30-50-2

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section 50
-Paragraph 11B
-Subparagraph (c)(1)
-SubTopic 10
-Topic 310
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481962/310-10-50-11B

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section 50
-Paragraph 11B
-Subparagraph (g)
-SubTopic 10
-Topic 310
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481962/310-10-50-11B

Reference 4: http://www.xbrl.org/2009/role/commonPracticeRef
-Name Accounting Standards Codification
-Section S99
-Paragraph 4
-Subparagraph (SAB Topic 6.L.1)
-SubTopic 10
-Topic 310
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480418/310-10-S99-4

+ Details

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

- Details

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

- Details

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

- Details

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

- Details

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

- Details

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

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=gnty_MultiFamilyResidentialPortfolioSegmentMember
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_FinancingReceivablePortfolioSegmentAxis=gnty_AgriculturalPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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