XML 260 R59.htm IDEA: XBRL DOCUMENT
v3.25.1

DISTRIBUTIONS TO COMMON STOCKHOLDERS - Schedule of Cash Distributions to Common Stockholders (Details) - $ / shares | 12 Months Ended
--- | ---
Mar. 31, 2025 | Mar. 31, 2024 | Mar. 31, 2023
Class of Stock [Line Items] |  |  |
Common stock dividends paid (in USD per share) | $ 1.66 | $ 2.20 | $ 1.410
O 2025 M1 Dividends |  |  |
Class of Stock [Line Items] |  |  |
Common stock, dividends, paid, ordinary (in USD per share) | 0.08 |  |
O 2025 M2 Dividends |  |  |
Class of Stock [Line Items] |  |  |
Common stock, dividends, paid, ordinary (in USD per share) | 0.08 |  |
O 2025 M3 Dividends |  |  |
Class of Stock [Line Items] |  |  |
Common stock, dividends, paid, ordinary (in USD per share) | 0.08 |  |
O 2025 M4 Dividends |  |  |
Class of Stock [Line Items] |  |  |
Common stock, dividends, paid, ordinary (in USD per share) | 0.08 |  |
O 2025 M5 Dividends |  |  |
Class of Stock [Line Items] |  |  |
Common stock, dividends, paid, ordinary (in USD per share) | 0.08 |  |
O 2025 M6 Dividends |  |  |
Class of Stock [Line Items] |  |  |
Common stock, dividends, paid, ordinary (in USD per share) | 0.08 |  |
O 2025 M7 Dividends |  |  |
Class of Stock [Line Items] |  |  |
Common stock, dividends, paid, ordinary (in USD per share) | 0.08 |  |
Common stock, dividends, paid, supplemental (in USD per share) | 0.70 |  |
O 2025 M8 Dividends |  |  |
Class of Stock [Line Items] |  |  |
Common stock, dividends, paid, ordinary (in USD per share) | 0.08 |  |
O 2025 M9 Dividends |  |  |
Class of Stock [Line Items] |  |  |
Common stock, dividends, paid, ordinary (in USD per share) | 0.08 |  |
O 2025 M10 Dividends |  |  |
Class of Stock [Line Items] |  |  |
Common stock, dividends, paid, ordinary (in USD per share) | 0.08 |  |
O 2025 M11 Dividends |  |  |
Class of Stock [Line Items] |  |  |
Common stock, dividends, paid, ordinary (in USD per share) | 0.08 |  |
O 2025 M12 Dividends |  |  |
Class of Stock [Line Items] |  |  |
Common stock, dividends, paid, ordinary (in USD per share) | $ 0.08 |  |
O 2024 M1 Dividends |  |  |
Class of Stock [Line Items] |  |  |
Common stock, dividends, paid, ordinary (in USD per share) |  | 0.08 |
O 2024 M2 Dividends |  |  |
Class of Stock [Line Items] |  |  |
Common stock, dividends, paid, ordinary (in USD per share) |  | 0.08 |
O 2024 M3 Dividends |  |  |
Class of Stock [Line Items] |  |  |
Common stock, dividends, paid, ordinary (in USD per share) |  | 0.08 |
Common stock, dividends, paid, supplemental (in USD per share) |  | 0.12 |
O 2024 M4 Dividends |  |  |
Class of Stock [Line Items] |  |  |
Common stock, dividends, paid, ordinary (in USD per share) |  | 0.08 |
O 2024 M5 Dividends |  |  |
Class of Stock [Line Items] |  |  |
Common stock, dividends, paid, ordinary (in USD per share) |  | 0.08 |
O 2024 M6 Dividends |  |  |
Class of Stock [Line Items] |  |  |
Common stock, dividends, paid, ordinary (in USD per share) |  | 0.08 |
Common stock, dividends, paid, supplemental (in USD per share) |  | 0.12 |
O 2024 M7 Dividends |  |  |
Class of Stock [Line Items] |  |  |
Common stock, dividends, paid, ordinary (in USD per share) |  | 0.08 |
O 2024 M8 Dividends |  |  |
Class of Stock [Line Items] |  |  |
Common stock, dividends, paid, ordinary (in USD per share) |  | 0.08 |
Common stock, dividends, paid, supplemental (in USD per share) |  | 0.12 |
O 2024 M9 Dividends |  |  |
Class of Stock [Line Items] |  |  |
Common stock, dividends, paid, ordinary (in USD per share) |  | 0.08 |
Common stock, dividends, paid, supplemental (in USD per share) |  | 0.88 |
O 2024 M10 Dividends |  |  |
Class of Stock [Line Items] |  |  |
Common stock, dividends, paid, ordinary (in USD per share) |  | 0.08 |
O 2024 M11 Dividends |  |  |
Class of Stock [Line Items] |  |  |
Common stock, dividends, paid, ordinary (in USD per share) |  | 0.08 |
O 2024 M12 Dividends |  |  |
Class of Stock [Line Items] |  |  |
Common stock, dividends, paid, ordinary (in USD per share) |  | $ 0.08 |
O 2023 M1 Dividends |  |  |
Class of Stock [Line Items] |  |  |
Common stock, dividends, paid, ordinary (in USD per share) |  |  | 0.075
O 2023 M2 Dividends |  |  |
Class of Stock [Line Items] |  |  |
Common stock, dividends, paid, ordinary (in USD per share) |  |  | 0.075
O 2023 M3 Dividends |  |  |
Class of Stock [Line Items] |  |  |
Common stock, dividends, paid, ordinary (in USD per share) |  |  | 0.075
Common stock, dividends, paid, supplemental (in USD per share) |  |  | 0.120
O 2023 M4 Dividends |  |  |
Class of Stock [Line Items] |  |  |
Common stock, dividends, paid, ordinary (in USD per share) |  |  | 0.075
O 2023 M5 Dividends |  |  |
Class of Stock [Line Items] |  |  |
Common stock, dividends, paid, ordinary (in USD per share) |  |  | 0.075
O 2023 M6 Dividends |  |  |
Class of Stock [Line Items] |  |  |
Common stock, dividends, paid, ordinary (in USD per share) |  |  | 0.075
O 2023 M7 Dividends |  |  |
Class of Stock [Line Items] |  |  |
Common stock, dividends, paid, ordinary (in USD per share) |  |  | 0.080
O 2023 M8 Dividends |  |  |
Class of Stock [Line Items] |  |  |
Common stock, dividends, paid, ordinary (in USD per share) |  |  | 0.080
O 2023 M9 Dividends |  |  |
Class of Stock [Line Items] |  |  |
Common stock, dividends, paid, ordinary (in USD per share) |  |  | 0.080
Common stock, dividends, paid, supplemental (in USD per share) |  |  | 0.120
O 2023 M10 Dividends |  |  |
Class of Stock [Line Items] |  |  |
Common stock, dividends, paid, ordinary (in USD per share) |  |  | 0.080
O 2023 M11 Dividends |  |  |
Class of Stock [Line Items] |  |  |
Common stock, dividends, paid, ordinary (in USD per share) |  |  | 0.080
O 2023 M12 Dividends |  |  |
Class of Stock [Line Items] |  |  |
Common stock, dividends, paid, ordinary (in USD per share) |  |  | 0.080
Common stock, dividends, paid, supplemental (in USD per share) |  |  | $ 0.240

X
- Definition Common Stock, Dividends, Per Share, Paid, Ordinary + References No definition available. + Details
Name: | gain_CommonStockDividendsPerSharePaidOrdinary
Namespace Prefix: | gain_
Data Type: | dtr-types:perShareItemType
Balance Type: | na
Period Type: | duration

X
- Definition Common Stock, Dividends, Per Share, Paid, Supplemental + References No definition available. + Details
Name: | gain_CommonStockDividendsPerSharePaidSupplemental
Namespace Prefix: | gain_
Data Type: | dtr-types:perShareItemType
Balance Type: | na
Period Type: | duration

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/exampleRef -Topic 505 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 13 -Subparagraph (d) -Publisher FASB -URI https://asc.fasb.org/1943274/2147481112/505-10-50-13 Reference 2: http://www.xbrl.org/2003/role/recommendedDisclosureRef -Topic 272 -SubTopic 10 -Name Accounting Standards Codification -Section 45 -Paragraph 3 -Publisher FASB -URI https://asc.fasb.org/1943274/2147483014/272-10-45-3 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Topic 272 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482987/272-10-50-1 Reference 4: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 235 -SubTopic 10 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.4-08(d)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480678/235-10-S99-1 Reference 5: http://www.xbrl.org/2003/role/disclosureRef -Topic 505 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 13 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org/1943274/2147481112/505-10-50-13 Reference 6: http://www.xbrl.org/2003/role/disclosureRef -Topic 505 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 13 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org/1943274/2147481112/505-10-50-13 Reference 7: http://www.xbrl.org/2003/role/disclosureRef -Topic 505 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 13 -Subparagraph (e) -Publisher FASB -URI https://asc.fasb.org/1943274/2147481112/505-10-50-13 Reference 8: http://www.xbrl.org/2003/role/disclosureRef -Topic 505 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 13 -Subparagraph (h) -Publisher FASB -URI https://asc.fasb.org/1943274/2147481112/505-10-50-13 Reference 9: http://www.xbrl.org/2003/role/disclosureRef -Topic 505 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 14 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org/1943274/2147481112/505-10-50-14 Reference 10: http://www.xbrl.org/2003/role/disclosureRef -Topic 505 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 18 -Subparagraph (c) -Publisher FASB -URI https://asc.fasb.org/1943274/2147481112/505-10-50-18 Reference 11: http://www.xbrl.org/2003/role/disclosureRef -Topic 210 -SubTopic 10 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(27)(b)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480566/210-10-S99-1 Reference 12: http://www.xbrl.org/2003/role/disclosureRef -Topic 210 -SubTopic 10 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(28)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480566/210-10-S99-1 Reference 13: http://www.xbrl.org/2003/role/disclosureRef -Topic 505 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Publisher FASB -URI https://asc.fasb.org/1943274/2147481112/505-10-50-2 Reference 14: http://www.xbrl.org/2003/role/disclosureRef -Topic 210 -SubTopic 10 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(29)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480566/210-10-S99-1 Reference 15: http://www.xbrl.org/2003/role/disclosureRef -Topic 946 -SubTopic 10 -Name Accounting Standards Codification -Section S99 -Paragraph 3 -Subparagraph (SX 210.6-03(i)(2)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147479886/946-10-S99-3 Reference 16: http://www.xbrl.org/2003/role/disclosureRef -Topic 946 -SubTopic 10 -Name Accounting Standards Codification -Section S99 -Paragraph 3 -Subparagraph (SX 210.6-03(i)(1)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147479886/946-10-S99-3 Reference 17: http://www.xbrl.org/2003/role/disclosureRef -Topic 946 -SubTopic 10 -Name Accounting Standards Codification -Section S99 -Paragraph 3 -Subparagraph (SX 210.6-03(i)(2)(i)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147479886/946-10-S99-3 Reference 18: http://www.xbrl.org/2003/role/disclosureRef -Topic 946 -SubTopic 10 -Name Accounting Standards Codification -Section S99 -Paragraph 3 -Subparagraph (SX 210.6-03(i)(2)(ii)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147479886/946-10-S99-3 + Details
Name: | us-gaap_ClassOfStockLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Aggregate dividends paid during the period for each share of common stock outstanding. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 505 -SubTopic 10 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.3-04) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480008/505-10-S99-1 + Details
Name: | us-gaap_CommonStockDividendsPerShareCashPaid
Namespace Prefix: | us-gaap_
Data Type: | dtr-types:perShareItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_DividendsAxis=gain_O2025M1DividendsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DividendsAxis=gain_O2025M2DividendsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DividendsAxis=gain_O2025M3DividendsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DividendsAxis=gain_O2025M4DividendsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DividendsAxis=gain_O2025M5DividendsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DividendsAxis=gain_O2025M6DividendsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DividendsAxis=gain_O2025M7DividendsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DividendsAxis=gain_O2025M8DividendsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DividendsAxis=gain_O2025M9DividendsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DividendsAxis=gain_O2025M10DividendsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DividendsAxis=gain_O2025M11DividendsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DividendsAxis=gain_O2025M12DividendsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DividendsAxis=gain_O2024M1DividendsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DividendsAxis=gain_O2024M2DividendsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DividendsAxis=gain_O2024M3DividendsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DividendsAxis=gain_O2024M4DividendsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DividendsAxis=gain_O2024M5DividendsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DividendsAxis=gain_O2024M6DividendsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DividendsAxis=gain_O2024M7DividendsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DividendsAxis=gain_O2024M8DividendsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DividendsAxis=gain_O2024M9DividendsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DividendsAxis=gain_O2024M10DividendsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DividendsAxis=gain_O2024M11DividendsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DividendsAxis=gain_O2024M12DividendsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DividendsAxis=gain_O2023M1DividendsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DividendsAxis=gain_O2023M2DividendsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DividendsAxis=gain_O2023M3DividendsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DividendsAxis=gain_O2023M4DividendsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DividendsAxis=gain_O2023M5DividendsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DividendsAxis=gain_O2023M6DividendsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DividendsAxis=gain_O2023M7DividendsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DividendsAxis=gain_O2023M8DividendsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DividendsAxis=gain_O2023M9DividendsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DividendsAxis=gain_O2023M10DividendsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DividendsAxis=gain_O2023M11DividendsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DividendsAxis=gain_O2023M12DividendsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |