N-2 $ in Millions	May 29, 2026 USD ($)
Cover [Abstract]
Entity Central Index Key	0001513363
Amendment Flag	false
Securities Act File Number	814-00861
Document Type	8-K
Entity Registrant Name	Fidus Investment Corporation
Entity Address, Address Line One	1603 Orrington Avenue
Entity Address, Address Line Two	Suite 1005
Entity Address, City or Town	Evanston
Entity Address, State or Province	IL
Entity Address, Postal Zip Code	60201
City Area Code	847
Local Phone Number	859-3940
Entity Emerging Growth Company	false
Capital Stock, Long-Term Debt, and Other Securities [Abstract]
Long Term Debt [Table Text Block]	In connection with the issuance and sale of the 6.625% Senior Unsecured Notes due June 1, 2029 (the “2029 Notes” and the issuance and sale of the 2029 Notes, the “Offering”) of Fidus Investment Corporation (the “Company”), the Company entered into a Registration Rights Agreement, dated as of May 29, 2026 (the “Registration Rights Agreement”), with the institutional purchasers in the Offering (the “Purchasers”). Pursuant to the Registration Rights Agreement, the Company is obligated to file with the Securities and Exchange Commission a registration statement with respect to an offer to exchange the 2029 Notes for a new issue of debt securities registered under the Securities Act of 1933, as amended (the “Securities Act”), with terms substantially identical to those of the 2029 Notes (except for provisions relating to transfer restrictions and payment of additional interest) and to use its commercially reasonable efforts to consummate such exchange offer on the earliest practicable date after the registration statement has been declared effective but in no event later than 365 days after the initial issuance of the 2029 Notes. If the Company fails to satisfy its registration obligations under the Registration Rights Agreement, the Company will be required to pay additional interest to the holder of the 2029 Notes. The description above is only a summary of the material provisions of the Registration Rights Agreement and is qualified in its entirety by reference to the Registration Rights Agreement, which is filed as Exhibit 4.1 hereto and incorporated by reference herein.
Long Term Debt, Title [Text Block]	6.625% Senior Unsecured Notes due June 1, 2029
Long Term Debt, Principal	$ 120.0
Long Term Debt, Dividends and Covenants [Text Block]	On May 29, 2026, the Company entered into a Note Purchase Agreement (the “Note Purchase Agreement”) with the Purchasers, which Note Purchase Agreement relates to the Company’s sale of $ 120.0 million in aggregate principal amount of the 2029 Notes to the Purchasers in a private placement in reliance on Section 4(a)(2) of the Securities Act. The Company is relying upon this exemption from registration based in part on representations made by the Purchasers. The Note Purchase Agreement also includes customary representations, warranties and covenants by the Company. The 2029 Notes have not been registered under the Securities Act and may not be offered or sold in the United States absent registration or an applicable exemption from registration.
Outstanding Securities [Table Text Block]	The 2029 Notes will mature on June 1, 2029 and may be redeemed in whole or in part at the Company’s option at any time prior to March 1, 2029 at par plus a “make-whole” premium, and thereafter at par. The 2029 Notes bear interest at a rate of 6.625% per year payable semi-annually on June 1 and December 1 of each year, commencing on December 1, 2026. The 2029 Notes are the Company’s direct unsecured obligations and rank: pari passu with the Company’s other outstanding and future unsecured, unsubordinated indebtedness; senior to any of the Company’s future indebtedness that expressly provides it is subordinated to the 2029 Notes; effectively subordinated to all of the Company’s existing and future secured indebtedness (including indebtedness that is initially unsecured in respect of which the Company has granted or subsequently grants security), to the extent of the value of the assets securing such indebtedness; and structurally subordinated to all existing and future indebtedness and other obligations of any of the Company’s subsidiaries. The closing of the private placement occurred on May 29, 2026. The net proceeds from the sale of the 2029 Notes were approximately $117.6 million, based on an offering price of 99.45% per Note, after deducting the placement agent fee of $1.5 million and estimated offering expenses of approximately $0.3 million, each payable by the Company. The Company intends to use the net proceeds from the Offering together with cash to fully redeem the Company’s outstanding 3.50% Notes due 2026 (CUSIP No. 316500 AC1) (the “2026 Notes”). Redemption of 2026 Notes On May 29, 2026, the Company caused notices to be issued to the holders of the 2026 Notes regarding the Company’s exercise of its option to redeem, in full, $125.0 million in aggregate principal amount of the issued and outstanding 2026 Notes, pursuant to Section 1104 of the Base Indenture and Section 1.01(h) of the Fifth Supplemental Indenture, dated as of October 8, 2021, by and between the Company and U.S. Bank Trust Company, National Association (as successor in interest to U.S. Bank National Association), as trustee. The Company will redeem $125.0 million in aggregate principal amount of the issued and outstanding 2026 Notes on June 29, 2026 (the “Redemption Date”). The redemption price for the 2026 Notes equals 100% of the $125.0 million aggregate principal amount of the 2026 Notes being redeemed on the Redemption Date, plus (i) accrued and unpaid interest to, but excluding, the Redemption Date and (ii) a “make-whole” premium. A copy of the notice of redemption of the 2026 Notes is filed as Exhibit 99.1 hereto and incorporated by reference herein.
Outstanding Security, Title [Text Block]	3.50% Notes due 2026

N-2
$ in Millions

May 29, 2026

USD ($)

Entity Central Index Key

0001513363

Amendment Flag

false

Securities Act File Number

814-00861

Document Type

8-K

Entity Registrant Name

Fidus Investment Corporation

Entity Address, Address Line One

1603 Orrington Avenue

Entity Address, Address Line Two

Suite 1005

Entity Address, City or Town

Evanston

Entity Address, State or Province

Entity Address, Postal Zip Code

60201

City Area Code

847

Local Phone Number

859-3940

Entity Emerging Growth Company

false

Capital Stock, Long-Term Debt, and Other Securities [Abstract]

Long Term Debt [Table Text Block]

In connection with the issuance and sale of the 6.625% Senior Unsecured Notes due June 1, 2029 (the “2029 Notes” and the issuance and sale of the 2029 Notes, the “Offering”) of Fidus Investment Corporation (the “Company”), the Company entered into a Registration Rights Agreement, dated as of May 29, 2026 (the “Registration Rights Agreement”), with the institutional purchasers in the Offering (the “Purchasers”). Pursuant to the Registration Rights Agreement, the Company is obligated to file with the Securities and Exchange Commission a registration statement with respect to an offer to exchange the 2029 Notes for a new issue of debt securities registered under the Securities Act of 1933, as amended (the “Securities Act”), with terms substantially identical to those of the 2029 Notes (except for provisions relating to transfer restrictions and payment of additional interest) and to use its commercially reasonable efforts to consummate such exchange offer on the earliest practicable date after the registration statement has been declared effective but in no event later than 365 days after the initial issuance of the 2029 Notes. If the Company fails to satisfy its registration obligations under the Registration Rights Agreement, the Company will be required to pay additional interest to the holder of the 2029 Notes.

The description above is only a summary of the material provisions of the Registration Rights Agreement and is qualified in its entirety by reference to the Registration Rights Agreement, which is filed as Exhibit 4.1 hereto and incorporated by reference herein.

Long Term Debt, Title [Text Block]

6.625% Senior Unsecured Notes due June 1, 2029

Long Term Debt, Principal

$ 120.0

Long Term Debt, Dividends and Covenants [Text Block]

On May 29, 2026, the Company entered into a Note Purchase Agreement (the “Note Purchase Agreement”) with the Purchasers, which Note Purchase Agreement relates to the Company’s sale of $

120.0

million in aggregate principal amount of the 2029 Notes to the Purchasers in a private placement in reliance on Section 4(a)(2) of the Securities Act. The Company is relying upon this exemption from registration based in part on representations made by the Purchasers. The Note Purchase Agreement also includes customary representations, warranties and covenants by the Company. The 2029 Notes have not been registered under the Securities Act and may not be offered or sold in the United States absent registration or an applicable exemption from registration.

Outstanding Securities [Table Text Block]

The 2029 Notes will mature on June 1, 2029 and may be redeemed in whole or in part at the Company’s option at any time prior to March 1, 2029 at par plus a “make-whole” premium, and thereafter at par. The 2029 Notes bear interest at a rate of 6.625% per year payable semi-annually on June 1 and December 1 of each year, commencing on December 1, 2026. The 2029 Notes are the Company’s direct unsecured obligations and rank:

pari passu

with the Company’s other outstanding and future unsecured, unsubordinated indebtedness; senior to any of the Company’s future indebtedness that expressly provides it is subordinated to the 2029 Notes; effectively subordinated to all of the Company’s existing and future secured indebtedness (including indebtedness that is initially unsecured in respect of which the Company has granted or subsequently grants security), to the extent of the value of the assets securing such indebtedness; and structurally subordinated to all existing and future indebtedness and other obligations of any of the Company’s subsidiaries.

The closing of the private placement occurred on May 29, 2026. The net proceeds from the sale of the 2029 Notes were approximately $117.6 million, based on an offering price of 99.45% per Note, after deducting the placement agent fee of $1.5 million and estimated offering expenses of approximately $0.3 million, each payable by the Company. The Company intends to use the net proceeds from the Offering together with cash to fully redeem the Company’s outstanding 3.50% Notes due 2026 (CUSIP No. 316500 AC1) (the “2026 Notes”).

Redemption of 2026 Notes

On May 29, 2026, the Company caused notices to be issued to the holders of the 2026 Notes regarding the Company’s exercise of its option to redeem, in full, $125.0 million in aggregate principal amount of the issued and outstanding 2026 Notes, pursuant to Section 1104 of the Base Indenture and Section 1.01(h) of the Fifth Supplemental Indenture, dated as of October 8, 2021, by and between the Company and U.S. Bank Trust Company, National Association (as successor in interest to U.S. Bank National Association), as trustee. The Company will redeem $125.0 million in aggregate principal amount of the issued and outstanding 2026 Notes on June 29, 2026 (the “Redemption Date”). The redemption price for the 2026 Notes equals 100% of the $125.0 million aggregate principal amount of the 2026 Notes being redeemed on the Redemption Date, plus (i) accrued and unpaid interest to, but excluding, the Redemption Date and (ii) a “make-whole” premium. A copy of the notice of redemption of the 2026 Notes is filed as Exhibit 99.1 hereto and incorporated by reference herein.

Outstanding Security, Title [Text Block]

3.50% Notes due 2026