XML 55 R49.htm IDEA: XBRL DOCUMENT
v3.25.3

Debt - Summary of Issued and Outstanding SBA Debentures (Details) - USD ($) $ in Thousands | 9 Months Ended |
--- | --- | ---
Sep. 30, 2025 | Dec. 31, 2024
Debt Instrument [Line Items] |  |
Total outstanding SBA debentures | $ 191,000 | $ 175,000
2.377% Fixed Interest Rate |  |
Debt Instrument [Line Items] |  |
Pooling Date | Sep. 25, 2019 |
Maturity Date | Sep. 01, 2029 |
Fixed Interest Rate | 2.377% |
Total outstanding SBA debentures | $ 7,500 | 7,500
2.172% Fixed Interest Rate |  |
Debt Instrument [Line Items] |  |
Pooling Date | Mar. 25, 2020 |
Maturity Date | Mar. 01, 2030 |
Fixed Interest Rate | 2.172% |
Total outstanding SBA debentures | $ 6,000 | 6,000
1.398% Fixed Interest Rate |  |
Debt Instrument [Line Items] |  |
Pooling Date | Sep. 22, 2021 |
Maturity Date | Sep. 01, 2031 |
Fixed Interest Rate | 1.398% |
Total outstanding SBA debentures | $ 11,500 | 11,500
3.209% Fixed Interest Rate |  |
Debt Instrument [Line Items] |  |
Pooling Date | Mar. 23, 2022 |
Maturity Date | Mar. 01, 2032 |
Fixed Interest Rate | 3.209% |
Total outstanding SBA debentures | $ 43,000 | 43,500
4.533% Fixed Interest Rate |  |
Debt Instrument [Line Items] |  |
Pooling Date | Sep. 21, 2022 |
Maturity Date | Sep. 01, 2032 |
Fixed Interest Rate | 4.533% |
Total outstanding SBA debentures | $ 17,500 | 17,500
5.439% Fixed Interest Rate |  |
Debt Instrument [Line Items] |  |
Pooling Date | Mar. 22, 2023 |
Maturity Date | Mar. 01, 2033 |
Fixed Interest Rate | 5.439% |
Total outstanding SBA debentures | $ 4,000 | 4,000
5.341% Fixed Interest Rate |  |
Debt Instrument [Line Items] |  |
Pooling Date | Mar. 22, 2023 |
Maturity Date | Mar. 01, 2033 |
Fixed Interest Rate | 5.341% |
Total outstanding SBA debentures | $ 3,000 | 3,000
5.341% Fixed Interest Rate |  |
Debt Instrument [Line Items] |  |
Pooling Date | Mar. 22, 2023 |
Maturity Date | Mar. 01, 2033 |
Fixed Interest Rate | 5.341% |
Total outstanding SBA debentures | $ 3,000 | 3,000
5.439% Fixed Interest Rate |  |
Debt Instrument [Line Items] |  |
Pooling Date | Mar. 22, 2023 |
Maturity Date | Mar. 01, 2033 |
Fixed Interest Rate | 5.439% |
Total outstanding SBA debentures | $ 5,000 | 5,000
5.439% Fixed Interest Rate |  |
Debt Instrument [Line Items] |  |
Pooling Date | Mar. 22, 2023 |
Maturity Date | Mar. 01, 2033 |
Fixed Interest Rate | 5.439% |
Total outstanding SBA debentures | $ 5,000 | 5,000
5.341% Fixed Interest Rate |  |
Debt Instrument [Line Items] |  |
Pooling Date | Mar. 22, 2023 |
Maturity Date | Mar. 01, 2033 |
Fixed Interest Rate | 5.341% |
Total outstanding SBA debentures | $ 7,000 | 7,000
5.341% Fixed Interest Rate |  |
Debt Instrument [Line Items] |  |
Pooling Date | Mar. 22, 2023 |
Maturity Date | Mar. 01, 2033 |
Fixed Interest Rate | 5.341% |
Total outstanding SBA debentures | $ 4,000 | 4,000
5.861% Fixed Interest Rate |  |
Debt Instrument [Line Items] |  |
Pooling Date | Sep. 20, 2023 |
Maturity Date | Sep. 01, 2033 |
Fixed Interest Rate | 5.861% |
Total outstanding SBA debentures | $ 5,000 | 8,000
5.861% Fixed Interest Rate |  |
Debt Instrument [Line Items] |  |
Pooling Date | Sep. 20, 2023 |
Maturity Date | Sep. 01, 2033 |
Fixed Interest Rate | 5.861% |
Total outstanding SBA debentures |  | 12,000
5.861% Fixed Interest Rate |  |
Debt Instrument [Line Items] |  |
Pooling Date | Sep. 20, 2023 |
Maturity Date | Sep. 01, 2033 |
Fixed Interest Rate | 5.861% |
Total outstanding SBA debentures |  | 5,000
5.861% Fixed Interest Rate |  |
Debt Instrument [Line Items] |  |
Pooling Date | Sep. 20, 2023 |
Maturity Date | Sep. 01, 2033 |
Fixed Interest Rate | 5.861% |
Total outstanding SBA debentures |  | 8,000
5.735% Fixed Interest Rate |  |
Debt Instrument [Line Items] |  |
Pooling Date | Sep. 20, 2023 |
Maturity Date | Sep. 01, 2033 |
Fixed Interest Rate | 5.735% |
Total outstanding SBA debentures | $ 3,000 | 3,000
5.082% Fixed Interest Rate |  |
Debt Instrument [Line Items] |  |
Pooling Date | Mar. 20, 2024 |
Maturity Date | Mar. 01, 2034 |
Fixed Interest Rate | 5.082% |
Total outstanding SBA debentures | $ 3,000 | 3,000
5.082% Fixed Interest Rate |  |
Debt Instrument [Line Items] |  |
Pooling Date | Mar. 20, 2024 |
Maturity Date | Mar. 01, 2034 |
Fixed Interest Rate | 5.082% |
Total outstanding SBA debentures | $ 12,000 | 12,000
5.082% Fixed Interest Rate |  |
Debt Instrument [Line Items] |  |
Pooling Date | Mar. 20, 2024 |
Maturity Date | Mar. 01, 2034 |
Fixed Interest Rate | 5.082% |
Total outstanding SBA debentures | $ 2,000 | 2,000
5.082% Fixed Interest Rate |  |
Debt Instrument [Line Items] |  |
Pooling Date | Mar. 20, 2024 |
Maturity Date | Mar. 01, 2034 |
Fixed Interest Rate | 5.082% |
Total outstanding SBA debentures | $ 2,000 | 2,000
5.082% Fixed Interest Rate |  |
Debt Instrument [Line Items] |  |
Pooling Date | Mar. 20, 2024 |
Maturity Date | Mar. 01, 2034 |
Fixed Interest Rate | 5.082% |
Total outstanding SBA debentures | $ 3,000 | $ 3,000
5.310% Fixed Interest Rate |  |
Debt Instrument [Line Items] |  |
Pooling Date | Mar. 26, 2025 |
Maturity Date | Mar. 01, 2035 |
Fixed Interest Rate | 5.31% |
Total outstanding SBA debentures | $ 19,500 |
4.879% Fixed Interest Rate |  |
Debt Instrument [Line Items] |  |
Pooling Date | Sep. 25, 2025 |
Maturity Date | Sep. 01, 2035 |
Fixed Interest Rate | 4.879% |
Total outstanding SBA debentures | $ 10,000 |
4.879% Fixed Interest Rate |  |
Debt Instrument [Line Items] |  |
Pooling Date | Sep. 25, 2025 |
Maturity Date | Sep. 01, 2035 |
Fixed Interest Rate | 4.879% |
Total outstanding SBA debentures | $ 10,000 |
4.74% Fixed Interest Rate |  |
Debt Instrument [Line Items] |  |
Total outstanding SBA debentures | $ 5,000 |

X
- Definition Debt instrument, pooling date. + References No definition available. + Details
Name: | fdus_DebtInstrumentPoolingDate
Namespace Prefix: | fdus_
Data Type: | xbrli:dateItemType
Balance Type: | na
Period Type: | duration

X
- Definition Face (par) amount of debt instrument at time of issuance. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Topic 835 -SubTopic 30 -Name Accounting Standards Codification -Section 55 -Paragraph 8 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482949/835-30-55-8 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 470 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1B -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org/1943274/2147481139/470-20-50-1B Reference 3: http://www.xbrl.org/2003/role/exampleRef -Topic 470 -SubTopic 20 -Name Accounting Standards Codification -Section 55 -Paragraph 69B -Publisher FASB -URI https://asc.fasb.org/1943274/2147481568/470-20-55-69B Reference 4: http://www.xbrl.org/2003/role/exampleRef -Topic 470 -SubTopic 20 -Name Accounting Standards Codification -Section 55 -Paragraph 69C -Publisher FASB -URI https://asc.fasb.org/1943274/2147481568/470-20-55-69C Reference 5: http://www.xbrl.org/2003/role/disclosureRef -Topic 835 -SubTopic 30 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482900/835-30-50-1 Reference 6: http://www.xbrl.org/2003/role/disclosureRef -Topic 835 -SubTopic 30 -Name Accounting Standards Codification -Section 45 -Paragraph 2 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482925/835-30-45-2 + Details
Name: | us-gaap_DebtInstrumentFaceAmount
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Contractual interest rate for funds borrowed, under the debt agreement. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 210 -SubTopic 10 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(22)(a)(1)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480566/210-10-S99-1 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 470 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1B -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org/1943274/2147481139/470-20-50-1B + Details
Name: | us-gaap_DebtInstrumentInterestRateStatedPercentage
Namespace Prefix: | us-gaap_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | instant

X
- 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 815 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 8A -Publisher FASB -URI https://asc.fasb.org/1943274/2147480434/815-10-50-8A Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 942 -SubTopic 235 -Name Accounting Standards Codification -Section S99 -Paragraph 2 -Publisher FASB -URI https://asc.fasb.org/1943274/2147477314/942-235-S99-2 Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 235 -SubTopic 10 -Name Accounting Standards Codification -Section S50 -Paragraph 1 -Publisher FASB -URI https://asc.fasb.org/1943274/2147480738/235-10-S50-1 Reference 4: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 235 -SubTopic 10 -Name Accounting Standards Codification -Section S50 -Paragraph 4 -Publisher FASB -URI https://asc.fasb.org/1943274/2147480738/235-10-S50-4 Reference 5: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 235 -SubTopic 10 -Name Accounting Standards Codification -Section S99 -Paragraph 3 -Subparagraph (SX 210.12-04(a)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480678/235-10-S99-3 Reference 6: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 235 -SubTopic 10 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.4-08(f)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480678/235-10-S99-1 Reference 7: http://www.xbrl.org/2003/role/exampleRef -Topic 835 -SubTopic 30 -Name Accounting Standards Codification -Section 55 -Paragraph 8 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482949/835-30-55-8 Reference 8: http://www.xbrl.org/2003/role/disclosureRef -Topic 470 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1B -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org/1943274/2147481139/470-20-50-1B Reference 9: http://www.xbrl.org/2003/role/exampleRef -Topic 470 -SubTopic 20 -Name Accounting Standards Codification -Section 55 -Paragraph 69B -Publisher FASB -URI https://asc.fasb.org/1943274/2147481568/470-20-55-69B Reference 10: http://www.xbrl.org/2003/role/exampleRef -Topic 470 -SubTopic 20 -Name Accounting Standards Codification -Section 55 -Paragraph 69C -Publisher FASB -URI https://asc.fasb.org/1943274/2147481568/470-20-55-69C Reference 11: http://www.xbrl.org/2003/role/exampleRef -Topic 470 -SubTopic 20 -Name Accounting Standards Codification -Section 55 -Paragraph 69E -Publisher FASB -URI https://asc.fasb.org/1943274/2147481568/470-20-55-69E Reference 12: http://www.xbrl.org/2003/role/exampleRef -Topic 470 -SubTopic 20 -Name Accounting Standards Codification -Section 55 -Paragraph 69F -Publisher FASB -URI https://asc.fasb.org/1943274/2147481568/470-20-55-69F Reference 13: http://www.xbrl.org/2003/role/disclosureRef -Topic 470 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1B -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org/1943274/2147481139/470-20-50-1B Reference 14: http://www.xbrl.org/2003/role/disclosureRef -Topic 470 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1B -Subparagraph (c) -Publisher FASB -URI https://asc.fasb.org/1943274/2147481139/470-20-50-1B Reference 15: http://www.xbrl.org/2003/role/exampleRef -Topic 470 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1B -Subparagraph (d) -Publisher FASB -URI https://asc.fasb.org/1943274/2147481139/470-20-50-1B Reference 16: http://www.xbrl.org/2003/role/disclosureRef -Topic 470 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1B -Subparagraph (e) -Publisher FASB -URI https://asc.fasb.org/1943274/2147481139/470-20-50-1B Reference 17: http://www.xbrl.org/2003/role/disclosureRef -Topic 470 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1B -Subparagraph (f) -Publisher FASB -URI https://asc.fasb.org/1943274/2147481139/470-20-50-1B Reference 18: http://www.xbrl.org/2003/role/disclosureRef -Topic 470 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1B -Subparagraph (h) -Publisher FASB -URI https://asc.fasb.org/1943274/2147481139/470-20-50-1B Reference 19: http://www.xbrl.org/2003/role/disclosureRef -Topic 470 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1D -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org/1943274/2147481139/470-20-50-1D Reference 20: http://www.xbrl.org/2003/role/disclosureRef -Topic 470 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1D -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org/1943274/2147481139/470-20-50-1D Reference 21: http://www.xbrl.org/2003/role/disclosureRef -Topic 470 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1D -Subparagraph (c) -Publisher FASB -URI https://asc.fasb.org/1943274/2147481139/470-20-50-1D Reference 22: http://www.xbrl.org/2003/role/disclosureRef -Topic 470 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1E -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org/1943274/2147481139/470-20-50-1E Reference 23: http://www.xbrl.org/2003/role/disclosureRef -Topic 470 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1E -Subparagraph (c) -Publisher FASB -URI https://asc.fasb.org/1943274/2147481139/470-20-50-1E Reference 24: http://www.xbrl.org/2003/role/disclosureRef -Topic 470 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1E -Subparagraph (d) -Publisher FASB -URI https://asc.fasb.org/1943274/2147481139/470-20-50-1E Reference 25: http://www.xbrl.org/2003/role/disclosureRef -Topic 470 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1F -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org/1943274/2147481139/470-20-50-1F Reference 26: http://www.xbrl.org/2003/role/disclosureRef -Topic 470 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1F -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org/1943274/2147481139/470-20-50-1F Reference 27: http://www.xbrl.org/2003/role/disclosureRef -Topic 470 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1F -Subparagraph (b)(1) -Publisher FASB -URI https://asc.fasb.org/1943274/2147481139/470-20-50-1F Reference 28: http://www.xbrl.org/2003/role/disclosureRef -Topic 470 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1F -Subparagraph (b)(2) -Publisher FASB -URI https://asc.fasb.org/1943274/2147481139/470-20-50-1F Reference 29: http://www.xbrl.org/2003/role/disclosureRef -Topic 470 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1I -Subparagraph (c) -Publisher FASB -URI https://asc.fasb.org/1943274/2147481139/470-20-50-1I Reference 30: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 835 -SubTopic 30 -Name Accounting Standards Codification -Section 45 -Paragraph 2 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482925/835-30-45-2 Reference 31: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 835 -SubTopic 30 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482900/835-30-50-1 + Details
Name: | us-gaap_DebtInstrumentLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Date when the debt instrument is scheduled to be fully repaid, in YYYY-MM-DD format. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 820 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (bbb)(2)(i) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482106/820-10-50-2 Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 820 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (bbb)(2) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482106/820-10-50-2 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Topic 210 -SubTopic 10 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(22)(a)(2)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480566/210-10-S99-1 Reference 4: http://www.xbrl.org/2003/role/exampleRef -Topic 470 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1B -Subparagraph (d) -Publisher FASB -URI https://asc.fasb.org/1943274/2147481139/470-20-50-1B + Details
Name: | us-gaap_DebtInstrumentMaturityDate
Namespace Prefix: | us-gaap_
Data Type: | xbrli:dateItemType
Balance Type: | na
Period Type: | duration

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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