v3.25.4

N-2 - $ / shares | 9 Months Ended |  |  |
--- | --- | --- | --- | ---
Dec. 31, 2025 | Mar. 31, 2025 | Dec. 31, 2024 | Mar. 31, 2024
Cover [Abstract] |  |  |  |
Entity Central Index Key | 0000017313 |  |  |
Amendment Flag | false |  |  |
Securities Act File Number | 814-00061 |  |  |
Document Type | 10-Q |  |  |
Entity Registrant Name | CAPITAL SOUTHWEST CORPORATION |  |  |
Entity Address, Address Line One | 8333 Douglas Avenue |  |  |
Entity Address, Address Line Two | Suite 1100 |  |  |
Entity Address, City or Town | Dallas |  |  |
Entity Address, State or Province | TX |  |  |
Entity Address, Postal Zip Code | 75225 |  |  |
City Area Code | 214 |  |  |
Local Phone Number | 238-5700 |  |  |
Entity Emerging Growth Company | false |  |  |
General Description of Registrant [Abstract] |  |  |  |
Investment Objectives and Practices [Text Block] | We are an internally managed closed-end, non-diversified management investment company that has elected to be regulated as a BDC under the 1940 Act. We specialize in providing customized debt and equity financing to LMM companies in a broad range of investment segments located primarily in the United States. Our investment objective is to produce attractive risk-adjusted returns by generating current income from our debt investments and capital appreciation from our equity and equity related investments. Our investment strategy is to partner with business owners, management teams and financial sponsors to provide flexible financing solutions to fund growth, changes of control, or other corporate events. We invest primarily in first lien debt securities, secured by security interests in portfolio company assets. We also may invest in equity interests in our portfolio companies alongside our debt securities. We focus on investing in companies with histories of generating revenues and positive cash flow, established market positions and proven management teams with strong operating discipline. We primarily target senior debt and equity investments in LMM companies. Our target companies typically have annual EBITDA between $3.0 million and $25.0 million, and our investments generally range in size from $5.0 million to $50.0 million. We seek to fill the financing gap for LMM companies, which, historically, have had more limited access to financing from commercial banks and other traditional sources. The underserved nature of the LMM creates the opportunity for us to meet the financing needs of LMM companies while also negotiating favorable transaction terms and equity participations. Our ability to invest across a LMM company’s capital structure, from secured loans to equity securities, allows us to offer portfolio companies a comprehensive suite of financing options. Providing customized financing solutions is important to LMM companies. We generally seek to partner directly with financial sponsors, entrepreneurs, management teams and business owners in making our investments. Our LMM debt investments typically include senior loans with a first lien on the assets of the portfolio company. Our LMM debt investments typically have a term of up to five years from the original investment date. We also often seek to invest in the equity securities of our LMM portfolio companies. Because we are internally managed, we do not pay any external investment advisory fees, but instead directly incur the operating costs associated with employing investment and portfolio management professionals. We believe that our internally managed structure provides us with a beneficial operating expense structure when compared to other publicly traded and privately held investment firms that are externally managed, and our internally managed structure allows us the opportunity to leverage our non-interest operating expenses as we grow our investment portfolio. As of December 31, 2025 and 2024, the ratio of our last twelve months ("LTM") operating expenses, excluding interest expense, as a percentage of our LTM average total assets was 1.67% and 1.61%, respectively. |  |  |
NAV Per Share | $ 16.75 | $ 16.70 | $ 16.59 | $ 16.77
Capital Stock, Long-Term Debt, and Other Securities [Abstract] |  |  |  |
Long Term Debt [Table Text Block] | Credit Facilities As of December 31, 2025, we had $210.0 million borrowings outstanding and $299.2 million of undrawn commitments under the Corporate Credit Facility, and $104.0 million outstanding and $96.0 million of undrawn commitments under the SPV Credit Facility. Availability under the Credit Facilities is subject to certain leverage and borrowing base limitations, various covenants, reporting requirements and other customary requirements for similar credit facilities. For more information on our Credit Facilities, including material terms and financial covenants, refer to Note 5 - Borrowings in the Notes to the Consolidated Financial Statements. Unsecured Notes In December 2020, the Company issued $75.0 million in aggregate principal amount of 4.50% notes due 2026 (the "January 2026 Notes"). In February 2021, the Company issued an additional $65.0 million in aggregate principal amount of the January 2026 Notes. On December 9, 2024, the Company redeemed $140.0 million in aggregate principal amount of the issued and outstanding January 2026 Notes in full. The January 2026 Notes were redeemed at 100% of their principal amount, plus the accrued and unpaid interest thereon, through, but excluding the redemption date. Accordingly, the Company recognized a realized loss on extinguishment of debt, equal to the write-off of the related unamortized debt issuance costs, of $0.4 million during the year ended March 31, 2025. In August 2021, the Company issued $100.0 million in aggregate principal amount of 3.375% notes due 2026 (the "October 2026 Notes"). In November 2021, the Company issued an additional $50.0 million in aggregate principal amount of the October 2026 Notes. On October 13, 2025, the Company redeemed $150.0 million in aggregate principal amount of the issued and outstanding October 2026 Notes in full. The October 2026 Notes were redeemed at 100% of their principal amount, plus the accrued and unpaid interest thereon, through, but excluding the redemption date. Accordingly, the Company recognized a realized loss on extinguishment of debt, equal to the write-off of the related unamortized debt issuance costs, of $0.8 million during the quarter ended December 31, 2025. In June 2023, the Company issued approximately $71.9 million in aggregate principal amount, including the underwriters' full exercise of their option to purchase an additional $9.4 million in aggregate principal amount to cover over-allotments, of 7.75% notes due 2028 (the "August 2028 Notes"). On October 13, 2025, the Company redeemed $71.9 million in aggregate principal amount of the issued and outstanding August 2028 Notes in full. The August 2028 Notes were redeemed at 100% of their principal amount, plus the accrued and unpaid interest thereon, through, but excluding the redemption date. Accordingly, the Company recognized a realized loss on extinguishment of debt, equal to the write-off of the related unamortized debt issuance costs, of $1.4 million during the quarter ended December 31, 2025. In November 2024, the Company issued $230.0 million in aggregate principal amount of 5.125% convertible notes due 2029 (the "2029 Convertible Notes"), including the underwriters' full exercise of their option to purchase an additional $30.0 million in aggregate principal amount to cover over-allotments. The outstanding aggregate principal amount of the 2029 Convertible Notes as of both December 31, 2025 and March 31, 2025 was $230.0 million. In September 2025, the Company issued $350.0 million in aggregate principal amount of 5.950% notes due 2030 ("the September 2030 Notes"). The outstanding aggregate principal amount of the September 2030 Notes as of December 31, 2025 was $350.0 million. For more information on each of the January 2026 Notes, the October 2026 Notes, the August 2028 Notes, the 2029 Convertible Notes, and the September 2030 Notes, including material terms governing the unsecured notes, refer to Note 5 - Borrowings in the Notes to the Consolidated Financial Statements. SBA Debentures On April 20, 2021 and April 17, 2025, SBIC I and SBIC II, respectively, received a license from the SBA to operate as an SBIC under Section 301(c) of the Small Business Investment Act of 1958, as amended. The licenses allow each of SBIC I and SBIC II to obtain leverage by issuing SBA Debentures, subject to the issuance of a leverage commitment by the SBA. Current SBA regulations permit SBIC I and SBIC II to each borrow up to $175 million in SBA Debentures with at least $87.5 million in regulatory capital (as defined in the SBA regulations). As of December 31, 2025, SBIC I had a total leverage commitment from the SBA in the amount of $175.0 million, all of which was drawn. As of December 31, 2025, SBIC II had a total leverage commitment from the SBA in the amount of $40.0 million, of which $20.0 million was drawn. SBA Debentures have interest payable semi-annually and a ten-year maturity. The interest rate is fixed shortly after issuance at a market-driven spread over U.S. Treasury Notes with ten-year maturities. Interest on SBA Debentures is payable semi-annually on March 1 and September 1. The first maturity date related to the SBA Debentures occurs in September 2031. For more information on the SBA Debentures, refer to Note 5 - Borrowings in the Notes to the Consolidated Financial Statements. |  |  |
Credit Facility [Member] |  |  |  |
Capital Stock, Long-Term Debt, and Other Securities [Abstract] |  |  |  |
Long Term Debt, Title [Text Block] | Credit Facilities |  |  |
Long Term Debt, Structuring [Text Block] | As of December 31, 2025, we had $210.0 million borrowings outstanding and $299.2 million of undrawn commitments under the Corporate Credit Facility, and $104.0 million outstanding and $96.0 million of undrawn commitments under the SPV Credit Facility. Availability under the Credit Facilities is subject to certain leverage and borrowing base limitations, various covenants, reporting requirements and other customary requirements for similar credit facilities. For more information on our Credit Facilities, including material terms and financial covenants, refer to Note 5 - Borrowings in the Notes to the Consolidated Financial Statements. |  |  |
Long Term Debt, Dividends and Covenants [Text Block] | Availability under the Credit Facilities is subject to certain leverage and borrowing base limitations, various covenants, reporting requirements and other customary requirements for similar credit facilities. |  |  |
January 2026 Notes [Member] |  |  |  |
Capital Stock, Long-Term Debt, and Other Securities [Abstract] |  |  |  |
Long Term Debt, Title [Text Block] | Unsecured Notes |  |  |
Long Term Debt, Structuring [Text Block] | In December 2020, the Company issued $75.0 million in aggregate principal amount of 4.50% notes due 2026 (the "January 2026 Notes"). In February 2021, the Company issued an additional $65.0 million in aggregate principal amount of the January 2026 Notes. On December 9, 2024, the Company redeemed $140.0 million in aggregate principal amount of the issued and outstanding January 2026 Notes in full. The January 2026 Notes were redeemed at 100% of their principal amount, plus the accrued and unpaid interest thereon, through, but excluding the redemption date. Accordingly, the Company recognized a realized loss on extinguishment of debt, equal to the write-off of the related unamortized debt issuance costs, of $0.4 million during the year ended March 31, 2025. |  |  |
October 2026 Notes [Member] |  |  |  |
Capital Stock, Long-Term Debt, and Other Securities [Abstract] |  |  |  |
Long Term Debt, Structuring [Text Block] | In August 2021, the Company issued $100.0 million in aggregate principal amount of 3.375% notes due 2026 (the "October 2026 Notes"). In November 2021, the Company issued an additional $50.0 million in aggregate principal amount of the October 2026 Notes. On October 13, 2025, the Company redeemed $150.0 million in aggregate principal amount of the issued and outstanding October 2026 Notes in full. The October 2026 Notes were redeemed at 100% of their principal amount, plus the accrued and unpaid interest thereon, through, but excluding the redemption date. Accordingly, the Company recognized a realized loss on extinguishment of debt, equal to the write-off of the related unamortized debt issuance costs, of $0.8 million during the quarter ended December 31, 2025. |  |  |
August 2028 Notes [Member] |  |  |  |
Capital Stock, Long-Term Debt, and Other Securities [Abstract] |  |  |  |
Long Term Debt, Structuring [Text Block] | In June 2023, the Company issued approximately $71.9 million in aggregate principal amount, including the underwriters' full exercise of their option to purchase an additional $9.4 million in aggregate principal amount to cover over-allotments, of 7.75% notes due 2028 (the "August 2028 Notes"). On October 13, 2025, the Company redeemed $71.9 million in aggregate principal amount of the issued and outstanding August 2028 Notes in full. The August 2028 Notes were redeemed at 100% of their principal amount, plus the accrued and unpaid interest thereon, through, but excluding the redemption date. Accordingly, the Company recognized a realized loss on extinguishment of debt, equal to the write-off of the related unamortized debt issuance costs, of $1.4 million during the quarter ended December 31, 2025. |  |  |
2029 Convertible Notes [Member] |  |  |  |
Capital Stock, Long-Term Debt, and Other Securities [Abstract] |  |  |  |
Long Term Debt, Structuring [Text Block] | In November 2024, the Company issued $230.0 million in aggregate principal amount of 5.125% convertible notes due 2029 (the "2029 Convertible Notes"), including the underwriters' full exercise of their option to purchase an additional $30.0 million in aggregate principal amount to cover over-allotments. The outstanding aggregate principal amount of the 2029 Convertible Notes as of both December 31, 2025 and March 31, 2025 was $230.0 million. In September 2025, the Company issued $350.0 million in aggregate principal amount of 5.950% notes due 2030 ("the September 2030 Notes"). The outstanding aggregate principal amount of the September 2030 Notes as of December 31, 2025 was $350.0 million. |  |  |
SBA Debentures [Member] |  |  |  |
Capital Stock, Long-Term Debt, and Other Securities [Abstract] |  |  |  |
Long Term Debt, Title [Text Block] | SBA Debentures |  |  |
Long Term Debt, Structuring [Text Block] | On April 20, 2021 and April 17, 2025, SBIC I and SBIC II, respectively, received a license from the SBA to operate as an SBIC under Section 301(c) of the Small Business Investment Act of 1958, as amended. The licenses allow each of SBIC I and SBIC II to obtain leverage by issuing SBA Debentures, subject to the issuance of a leverage commitment by the SBA. Current SBA regulations permit SBIC I and SBIC II to each borrow up to $175 million in SBA Debentures with at least $87.5 million in regulatory capital (as defined in the SBA regulations). As of December 31, 2025, SBIC I had a total leverage commitment from the SBA in the amount of $175.0 million, all of which was drawn. As of December 31, 2025, SBIC II had a total leverage commitment from the SBA in the amount of $40.0 million, of which $20.0 million was drawn. SBA Debentures have interest payable semi-annually and a ten-year maturity. The interest rate is fixed shortly after issuance at a market-driven spread over U.S. Treasury Notes with ten-year maturities. Interest on SBA Debentures is payable semi-annually on March 1 and September 1. The first maturity date related to the SBA Debentures occurs in September 2031. For more information on the SBA Debentures, refer to Note 5 - Borrowings in the Notes to the Consolidated Financial Statements. |  |  |

X
- References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form N-2 -Section Item 10 + Details
Name: | cef_CapitalStockLongTermDebtAndOtherSecuritiesAbstract
Namespace Prefix: | cef_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form N-2 -Section Item 8 + Details
Name: | cef_GeneralDescriptionOfRegistrantAbstract
Namespace Prefix: | cef_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form N-2 -Section Item 8 -Subsection 2 -Paragraph b, d + Details
Name: | cef_InvestmentObjectivesAndPracticesTextBlock
Namespace Prefix: | cef_
Data Type: | dtr-types:textBlockItemType
Balance Type: | na
Period Type: | duration

X
- References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form N-2 -Section Item 10 -Subsection 2 -Paragraph b + Details
Name: | cef_LongTermDebtDividendsAndCovenantsTextBlock
Namespace Prefix: | cef_
Data Type: | dtr-types:textBlockItemType
Balance Type: | na
Period Type: | duration

X
- References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form N-2 -Section Item 10 -Subsection 2 -Paragraph a + Details
Name: | cef_LongTermDebtStructuringTextBlock
Namespace Prefix: | cef_
Data Type: | dtr-types:textBlockItemType
Balance Type: | na
Period Type: | duration

X
- References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form N-2 -Section Item 10 -Subsection 2 + Details
Name: | cef_LongTermDebtTableTextBlock
Namespace Prefix: | cef_
Data Type: | dtr-types:textBlockItemType
Balance Type: | na
Period Type: | duration

X
- References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form N-2 -Section Item 10 -Subsection 2 + Details
Name: | cef_LongTermDebtTitleTextBlock
Namespace Prefix: | cef_
Data Type: | dtr-types:textBlockItemType
Balance Type: | na
Period Type: | duration

X
- Definition Boolean flag that is true when the XBRL content amends previously-filed or accepted submission. + References No definition available. + Details
Name: | dei_AmendmentFlag
Namespace Prefix: | dei_
Data Type: | xbrli:booleanItemType
Balance Type: | na
Period Type: | duration

X
- Definition Area code of city + References No definition available. + Details
Name: | dei_CityAreaCode
Namespace Prefix: | dei_
Data Type: | xbrli:normalizedStringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Cover page. + References No definition available. + Details
Name: | dei_CoverAbstract
Namespace Prefix: | dei_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition The type of document being provided (such as 10-K, 10-Q, 485BPOS, etc). The document type is limited to the same value as the supporting SEC submission type, or the word 'Other'. + References No definition available. + Details
Name: | dei_DocumentType
Namespace Prefix: | dei_
Data Type: | dei:submissionTypeItemType
Balance Type: | na
Period Type: | duration

X
- Definition Address Line 1 such as Attn, Building Name, Street Name + References No definition available. + Details
Name: | dei_EntityAddressAddressLine1
Namespace Prefix: | dei_
Data Type: | xbrli:normalizedStringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Address Line 2 such as Street or Suite number + References No definition available. + Details
Name: | dei_EntityAddressAddressLine2
Namespace Prefix: | dei_
Data Type: | xbrli:normalizedStringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Name of the City or Town + References No definition available. + Details
Name: | dei_EntityAddressCityOrTown
Namespace Prefix: | dei_
Data Type: | xbrli:normalizedStringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Code for the postal or zip code + References No definition available. + Details
Name: | dei_EntityAddressPostalZipCode
Namespace Prefix: | dei_
Data Type: | xbrli:normalizedStringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Name of the state or province. + References No definition available. + Details
Name: | dei_EntityAddressStateOrProvince
Namespace Prefix: | dei_
Data Type: | dei:stateOrProvinceItemType
Balance Type: | na
Period Type: | duration

X
- Definition A unique 10-digit SEC-issued value to identify entities that have filed disclosures with the SEC. It is commonly abbreviated as CIK. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Exchange Act -Number 240 -Section 12 -Subsection b-2 + Details
Name: | dei_EntityCentralIndexKey
Namespace Prefix: | dei_
Data Type: | dei:centralIndexKeyItemType
Balance Type: | na
Period Type: | duration

X
- Definition Indicate if registrant meets the emerging growth company criteria. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Exchange Act -Number 240 -Section 12 -Subsection b-2 + Details
Name: | dei_EntityEmergingGrowthCompany
Namespace Prefix: | dei_
Data Type: | xbrli:booleanItemType
Balance Type: | na
Period Type: | duration

X
- Definition Commission file number. The field allows up to 17 characters. The prefix may contain 1-3 digits, the sequence number may contain 1-8 digits, the optional suffix may contain 1-4 characters, and the fields are separated with a hyphen. + References No definition available. + Details
Name: | dei_EntityFileNumber
Namespace Prefix: | dei_
Data Type: | dei:fileNumberItemType
Balance Type: | na
Period Type: | duration

X
- Definition The exact name of the entity filing the report as specified in its charter, which is required by forms filed with the SEC. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Exchange Act -Number 240 -Section 12 -Subsection b-2 + Details
Name: | dei_EntityRegistrantName
Namespace Prefix: | dei_
Data Type: | xbrli:normalizedStringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Local phone number for entity. + References No definition available. + Details
Name: | dei_LocalPhoneNumber
Namespace Prefix: | dei_
Data Type: | xbrli:normalizedStringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Net asset value per share or per unit of investments in certain entities that calculate net asset value per share. Includes, but is not limited to, by unit, membership interest, or other ownership interest. Investment includes, but is not limited to, investment in certain hedge funds, venture capital funds, private equity funds, real estate partnerships or funds. Excludes fair value disclosure. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Topic 946 -SubTopic 830 -Name Accounting Standards Codification -Section 55 -Paragraph 12 -Publisher FASB -URI https://asc.fasb.org/1943274/2147479168/946-830-55-12 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 946 -SubTopic 210 -Name Accounting Standards Codification -Section 45 -Paragraph 4 -Publisher FASB -URI https://asc.fasb.org/1943274/2147477796/946-210-45-4 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Topic 946 -SubTopic 205 -Name Accounting Standards Codification -Section 50 -Paragraph 7 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org/1943274/2147478494/946-205-50-7 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Topic 946 -SubTopic 205 -Name Accounting Standards Codification -Section 50 -Paragraph 7 -Subparagraph (h) -Publisher FASB -URI https://asc.fasb.org/1943274/2147478494/946-205-50-7 Reference 5: http://www.xbrl.org/2003/role/disclosureRef -Topic 946 -SubTopic 505 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Publisher FASB -URI https://asc.fasb.org/1943274/2147478448/946-505-50-1 Reference 6: http://www.xbrl.org/2003/role/disclosureRef -Topic 946 -SubTopic 210 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.6-04(19)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147479170/946-210-S99-1 Reference 7: http://www.xbrl.org/2003/role/disclosureRef -Topic 946 -SubTopic 210 -Name Accounting Standards Codification -Section S99 -Paragraph 2 -Subparagraph (SX 210.6-05(4)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147479170/946-210-S99-2 + Details
Name: | us-gaap_NetAssetValuePerShare
Namespace Prefix: | us-gaap_
Data Type: | dtr-types:perShareItemType
Balance Type: | na
Period Type: | instant

X
- Details
Name: | us-gaap_DebtInstrumentAxis=cswc_CreditFacilityMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DebtInstrumentAxis=cswc_January2026NotesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DebtInstrumentAxis=cswc_October2026NotesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DebtInstrumentAxis=cswc_August2028NotesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DebtInstrumentAxis=cswc_A2029ConvertibleNotesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DebtInstrumentAxis=cswc_SBADebenturesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |