Note 7 - Tax Status (Details Textual) - EBP 27-1560715 001 [Member]	12 Months Ended
Dec. 31, 2025
EBP, Tax Qualification Status [Extensible Enumeration]	Qualified Plan [Member]
true	true
EBP, Tax Determination Letter, Date	Jun. 30, 2020

Date of tax determination letter for employee stock purchase, saving, or similar plan (employee benefit plan (EBP)), in YYYY-MM-DD format.

Name:	us-gaap-ebp_EmployeeBenefitPlanTaxDeterminationLetterDate
Namespace Prefix:	us-gaap-ebp_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

Indicates (true false) whether tax determination letter was obtained by employer of participant in employee stock purchase, saving, or similar plan (employee benefit plan (EBP)).

+ References

+ Details

Name:	us-gaap-ebp_EmployeeBenefitPlanTaxDeterminationLetterObtained
Namespace Prefix:	us-gaap-ebp_
Data Type:	xbrli:booleanItemType
Balance Type:	na
Period Type:	duration

- Definition

Indicates tax qualification status of employee stock purchase, saving, or similar plan (employee benefit plan (EBP)).

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 962
-SubTopic 325
-Name Accounting Standards Codification
-Section 55
-Paragraph 17
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478873/962-325-55-17

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 962
-SubTopic 205
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (g)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478416/962-205-50-1

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 962
-SubTopic 205
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6A-02(c))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477804/962-205-S99-1

+ Details

Name:	us-gaap-ebp_EmployeeBenefitPlanTaxQualificationStatusExtensibleEnumeration
Namespace Prefix:	us-gaap-ebp_
Data Type:	enum2:enumerationSetItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	dei_LegalEntityAxis=istr_EBP271560715001Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: