LOANS AND ALLOWANCE FOR CREDIT LOSSES - Summary of Nonaccrual Loans (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Financing Receivable Nonaccrual Status [Line Items]
Nonaccrual Loans with No Related Allowance	$ 31,984	$ 29,245
Nonaccrual Loans with Related Allowance	25,145	9,946
Total Nonaccrual Loans	57,129	39,191
Commercial and industrial
Financing Receivable Nonaccrual Status [Line Items]
Nonaccrual Loans with No Related Allowance	1,073	1,616
Nonaccrual Loans with Related Allowance	14,392	3,432
Total Nonaccrual Loans	15,465	5,048
Paycheck Protection Program (PPP)
Financing Receivable Nonaccrual Status [Line Items]
Nonaccrual Loans with No Related Allowance	0	0
Nonaccrual Loans with Related Allowance	0	0
Total Nonaccrual Loans	0	0
Real estate: \| Commercial real estate (including multi-family residential)
Financing Receivable Nonaccrual Status [Line Items]
Nonaccrual Loans with No Related Allowance	15,905	11,844
Nonaccrual Loans with Related Allowance	5,363	4,855
Total Nonaccrual Loans	21,268	16,699
Real estate: \| Commercial real estate construction and land development
Financing Receivable Nonaccrual Status [Line Items]
Nonaccrual Loans with No Related Allowance	7,664	5,043
Nonaccrual Loans with Related Allowance	742	0
Total Nonaccrual Loans	8,406	5,043
Real estate: \| 1-4 family residential (including home equity)
Financing Receivable Nonaccrual Status [Line Items]
Nonaccrual Loans with No Related Allowance	7,310	7,400
Nonaccrual Loans with Related Allowance	3,058	1,474
Total Nonaccrual Loans	10,368	8,874
Real estate: \| Residential construction
Financing Receivable Nonaccrual Status [Line Items]
Nonaccrual Loans with No Related Allowance	0	3,288
Nonaccrual Loans with Related Allowance	1,410	0
Total Nonaccrual Loans	1,410	3,288
Consumer and other
Financing Receivable Nonaccrual Status [Line Items]
Nonaccrual Loans with No Related Allowance	32	54
Nonaccrual Loans with Related Allowance	180	185
Total Nonaccrual Loans	$ 212	$ 239

Financing Receivable, Nonaccrual, With Related Allowance

No definition available.

Name:	stel_FinancingReceivableNonaccrualWithRelatedAllowance
Namespace Prefix:	stel_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amortized cost of financing receivable on nonaccrual status with no allowance for credit loss. Excludes net investment in lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 16
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479319/326-20-50-16

+ Details

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

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 16
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479319/326-20-50-16

+ Details

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

- Definition

Amortized cost of financing receivable on nonaccrual status. Excludes net investment in lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 16
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479319/326-20-50-16

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Name Regulation S-K (SK)
-Number 229
-Section 1405
-Paragraph (a)
-Subparagraph (3)
-Publisher SEC

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Name Regulation S-K (SK)
-Number 229
-Section 1405
-Paragraph (a)
-Subparagraph (2)
-Publisher SEC

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 7
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481962/310-10-50-7

+ Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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=stel_PaycheckProtectionProgramPPPMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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

- Details

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

- Details

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

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=stel_ResidentialConstructionMember
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: