Debt - Additional Information (Details) |
1 Months Ended | 12 Months Ended | ||||||||||||||
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Oct. 27, 2020
USD ($)
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Jan. 31, 2023
USD ($)
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Dec. 31, 2023
USD ($)
Facility
investment
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Dec. 31, 2022
USD ($)
investment
Facility
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Jan. 13, 2023
USD ($)
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Jun. 23, 2022
USD ($)
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Jun. 22, 2022
USD ($)
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Jan. 20, 2022
USD ($)
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Dec. 31, 2021
USD ($)
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Sep. 16, 2021
USD ($)
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Mar. 04, 2021
USD ($)
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Nov. 04, 2020
USD ($)
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Jun. 03, 2020
USD ($)
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Feb. 05, 2020
USD ($)
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Jul. 16, 2019
USD ($)
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Sep. 24, 2018
USD ($)
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| Debt Instrument [Line Items] | ||||||||||||||||
| Outstanding balance | $ 2,215,000,000 | $ 2,185,000,000 | ||||||||||||||
| Investments at fair value | 3,248,046,000 | 2,963,955,000 | ||||||||||||||
| Restricted cash | $ 17,114,000 | $ 10,079,000 | $ 3,150,000 | |||||||||||||
| Number of available credit facilities | Facility | 2 | 2 | ||||||||||||||
| VIE | ||||||||||||||||
| Debt Instrument [Line Items] | ||||||||||||||||
| Restricted cash | $ 17,114,000 | $ 10,079,000 | ||||||||||||||
| MUFG Bank Facility | ||||||||||||||||
| Debt Instrument [Line Items] | ||||||||||||||||
| Maximum borrowing capacity | $ 400,000.0 | |||||||||||||||
| Line of credit facility, covenant terms | these covenants require the Company to maintain certain financial ratios, including a minimum interest coverage ratio and a minimum tangible net worth with respect to Hercules Funding IV | |||||||||||||||
| Line of credit facility, termination date | Jan. 13, 2026 | |||||||||||||||
| Line of credit facility, description | funded by existing or additional lenders and with the agreement of MUFG Bank and subject to other customary conditions. | |||||||||||||||
| MUFG Bank Facility | 1-month SOFR | ||||||||||||||||
| Debt Instrument [Line Items] | ||||||||||||||||
| Interest rate plus applicable margin adjustment | 2.75% | |||||||||||||||
| SMBC Facility | ||||||||||||||||
| Debt Instrument [Line Items] | ||||||||||||||||
| Maximum borrowing capacity | $ 175,000,000.0 | $ 225,000,000 | ||||||||||||||
| Line of credit facility, termination date | Jan. 13, 2026 | Nov. 09, 2026 | ||||||||||||||
| Line of credit facility, description | Availability under the SMBC Facility will terminate on November 7, 2025, and the outstanding loans under the SMBC Facility will mature on November 9, 2026 | |||||||||||||||
| Line of credit facility, unused capacity, commitment fee percentage | 0.375% | |||||||||||||||
| SMBC Facility | Minimum | ||||||||||||||||
| Debt Instrument [Line Items] | ||||||||||||||||
| Interest rate plus applicable margin adjustment | 0.875% | |||||||||||||||
| SMBC Facility | Maximum | ||||||||||||||||
| Debt Instrument [Line Items] | ||||||||||||||||
| Maximum borrowing capacity | $ 400,000,000.0 | $ 500,000,000.0 | ||||||||||||||
| Interest rate plus applicable margin adjustment | 2.00% | |||||||||||||||
| Revolving Credit Facility | ||||||||||||||||
| Debt Instrument [Line Items] | ||||||||||||||||
| Line of credit interest rate | 7.41% | 4.51% | ||||||||||||||
| Debt average amount outstanding | $ 192,300,000 | $ 127,700,000 | ||||||||||||||
| SBA Debentures | ||||||||||||||||
| Debt Instrument [Line Items] | ||||||||||||||||
| Outstanding balance | 175,000,000 | 175,000,000 | ||||||||||||||
| July 2024 Notes | ||||||||||||||||
| Debt Instrument [Line Items] | ||||||||||||||||
| Outstanding balance | $ 105,000,000 | 105,000,000 | $ 105,000,000 | |||||||||||||
| Debt Instrument, redemption, description | On July 16, 2019, the Company issued $105.0 million in aggregate principal amount of 4.77% interest-bearing unsecured notes due on July 16, 2024 (the “July 2024 Notes”), unless repurchased in accordance with their terms, to qualified institutional investors in a private placement notes offering. | |||||||||||||||
| Debt instrument, interest rate | 4.77% | |||||||||||||||
| Debt retired | Jul. 16, 2024 | |||||||||||||||
| Debt instrument, payment terms, description | Interest on the July 2024 Notes is due semiannually. | |||||||||||||||
| Debt instrument, collateral | The July 2024 Notes are general unsecured obligations of the Company that rank pari passu with all outstanding and future unsecured unsubordinated indebtedness issued by the Company. | |||||||||||||||
| February 2025 Notes | ||||||||||||||||
| Debt Instrument [Line Items] | ||||||||||||||||
| Outstanding balance | $ 50,000,000 | 50,000,000 | $ 50,000,000 | |||||||||||||
| Debt Instrument, redemption, description | On February 5, 2020, the Company issued $50.0 million in aggregate principal amount of 4.28% interest-bearing unsecured notes due February 5, 2025 (the “February 2025 Notes”), unless repurchased in accordance with their terms, to qualified institutional investors in a private placement notes offering. | |||||||||||||||
| Debt instrument, interest rate | 4.28% | |||||||||||||||
| Debt retired | Feb. 05, 2025 | |||||||||||||||
| Debt instrument, payment terms, description | Interest on the February 2025 Notes is due semiannually. | |||||||||||||||
| Debt instrument, collateral | The February 2025 Notes are general unsecured obligations of the Company that rank pari passu with all outstanding and future unsecured unsubordinated indebtedness issued by the Company. | |||||||||||||||
| June 2025 Notes | ||||||||||||||||
| Debt Instrument [Line Items] | ||||||||||||||||
| Outstanding balance | $ 70,000,000 | 70,000,000 | $ 70,000,000 | |||||||||||||
| Debt Instrument, redemption, description | On June 3, 2020, the Company issued $70.0 million in aggregate principal amount of 4.31% interest-bearing unsecured notes due June 3, 2025 (the “June 2025 Notes”), unless repurchased in accordance with their terms, to qualified institutional investors in a private placement notes offering. | |||||||||||||||
| Debt instrument, interest rate | 4.31% | |||||||||||||||
| Debt retired | Jun. 03, 2025 | |||||||||||||||
| Debt instrument, payment terms, description | Interest on the June 2025 Notes is due semiannually. | |||||||||||||||
| Debt instrument, collateral | The June 2025 Notes are general unsecured obligations of the Company that rank pari passu with all outstanding and future unsecured unsubordinated indebtedness issued by the Company. | |||||||||||||||
| June 2025 3-Year Notes | ||||||||||||||||
| Debt Instrument [Line Items] | ||||||||||||||||
| Outstanding balance | $ 50,000,000 | 50,000,000 | $ 50,000,000 | |||||||||||||
| Debt Instrument, redemption, description | On June 23, 2022, the Company issued $50.0 million in aggregate principal amount of 6.00% interest-bearing unsecured notes due June 23, 2025 (the “June 2025 3-Year Notes”), unless repurchased in accordance with their terms, to qualified institutional investors in a private placement notes offering. | |||||||||||||||
| Debt instrument, interest rate | 6.00% | |||||||||||||||
| Debt retired | Jun. 23, 2025 | |||||||||||||||
| Debt instrument, payment terms, description | Interest on the June 2025 3-Year Notes is due semiannually. | |||||||||||||||
| Debt instrument, collateral | The June 2025 3-Year Notes are general unsecured obligations of the Company that rank pari passu with all outstanding and future unsecured unsubordinated indebtedness issued by the Company. | |||||||||||||||
| March 2026 A Notes | ||||||||||||||||
| Debt Instrument [Line Items] | ||||||||||||||||
| Outstanding balance | $ 50,000,000 | 50,000,000 | $ 50,000,000 | |||||||||||||
| Debt Instrument, redemption, description | On November 4, 2020, the Company issued $50.0 million in aggregate principal amount of 4.50% interest-bearing unsecured notes due March 4, 2026 (the “March 2026 A Notes”), unless repurchased in accordance with their terms, to qualified institutional investors in a private placement notes offering. | |||||||||||||||
| Debt instrument, interest rate | 4.50% | |||||||||||||||
| Debt retired | Mar. 04, 2026 | |||||||||||||||
| Debt instrument, payment terms, description | Interest on the March 2026 A Notes is due semiannually. | |||||||||||||||
| Debt instrument, collateral | The March 2026 A Notes are general unsecured obligations of the Company that rank pari passu with all outstanding and future unsecured unsubordinated indebtedness issued by the Company. | |||||||||||||||
| March 2026 B Notes | ||||||||||||||||
| Debt Instrument [Line Items] | ||||||||||||||||
| Outstanding balance | $ 50,000,000 | 50,000,000 | $ 50,000,000 | |||||||||||||
| Debt Instrument, redemption, description | On March 4, 2021, the Company issued $50.0 million in aggregate principal amount of 4.55% interest-bearing unsecured notes due March 4, 2026 (the “March 2026 B Notes”), unless repurchased in accordance with their terms, to qualified institutional investors in a private placement pursuant note offering. | |||||||||||||||
| Debt instrument, interest rate | 4.55% | |||||||||||||||
| Debt retired | Mar. 04, 2026 | |||||||||||||||
| Debt instrument, payment terms, description | Interest on the March 2026 B Notes is due semiannually. | |||||||||||||||
| Debt instrument, collateral | The March 2026 B Notes are general unsecured obligations of the Company that rank pari passu with all outstanding and future unsecured unsubordinated indebtedness issued by the Company. | |||||||||||||||
| September 2026 Notes | ||||||||||||||||
| Debt Instrument [Line Items] | ||||||||||||||||
| Outstanding balance | $ 325,000,000 | 325,000,000 | $ 325,000,000 | |||||||||||||
| Debt instrument, interest rate | 2.625% | |||||||||||||||
| Debt retired | Sep. 16, 2026 | |||||||||||||||
| Debt instrument, payment terms, description | Interest on the September 2026 Notes is payable semi-annually in arrears on March 16 and September 16 of each year. | |||||||||||||||
| Debt instrument, collateral | The September 2026 Notes are general unsecured obligations and rank pari passu, or equally in right of payment, with all outstanding and future unsecured unsubordinated indebtedness issued by the Company. | |||||||||||||||
| January 2027 Notes | ||||||||||||||||
| Debt Instrument [Line Items] | ||||||||||||||||
| Outstanding balance | $ 350,000,000 | 350,000,000 | $ 350,000,000 | |||||||||||||
| Debt Instrument, redemption, description | The Company may redeem some or all of the January 2027 Notes at any time, or from time to time, at the redemption price set forth under the terms of the January 2027 Notes Indenture. | |||||||||||||||
| Debt instrument, interest rate | 3.375% | |||||||||||||||
| Debt retired | Jan. 20, 2027 | |||||||||||||||
| Debt instrument, payment terms, description | Interest on the January 2027 Notes is payable semi-annually in arrears on January 20 and July 20 of each year. | |||||||||||||||
| Debt instrument, collateral | The January 2027 Notes are general unsecured obligations and rank pari passu, or equally in right of payment, with all outstanding and future unsecured unsubordinated indebtedness issued by the Company. | |||||||||||||||
| 2031 Asset-Backed Notes | ||||||||||||||||
| Debt Instrument [Line Items] | ||||||||||||||||
| Outstanding balance | $ 150,000,000 | 150,000,000 | $ 150,000,000 | |||||||||||||
| Debt instrument, interest rate | 4.95% | |||||||||||||||
| Debt retired | Jul. 20, 2031 | |||||||||||||||
| Debt instrument, payment terms, description | Interest on the 2031 Asset-Backed Notes will be paid, to the extent of funds available. | |||||||||||||||
| 2031 Asset-Backed Notes | VIE | ||||||||||||||||
| Debt Instrument [Line Items] | ||||||||||||||||
| Restricted cash | $ 17,100,000 | 10,100,000 | ||||||||||||||
| 2033 Notes | ||||||||||||||||
| Debt Instrument [Line Items] | ||||||||||||||||
| Outstanding balance | $ 40,000,000 | 40,000,000 | $ 40,000,000 | |||||||||||||
| Debt Instrument, redemption, description | The Company may redeem some or all of the 2033 Notes at any time, or from time to time, at the redemption price set forth under the terms of the 2033 Notes indenture after October 30, 2023. | |||||||||||||||
| Debt instrument, interest rate | 6.25% | |||||||||||||||
| Debt retired | Oct. 30, 2033 | |||||||||||||||
| Debt instrument, payment terms, description | Interest on the 2033 Notes is payable quarterly in arrears on January 30, April 30, July 30, and October 30 of each year. | |||||||||||||||
| SMBC Facility | ||||||||||||||||
| Debt Instrument [Line Items] | ||||||||||||||||
| Outstanding balance | $ 400,000,000 | 225,000,000 | ||||||||||||||
| MUFG Bank Facility | ||||||||||||||||
| Debt Instrument [Line Items] | ||||||||||||||||
| Outstanding balance | $ 400,000,000 | $ 545,000,000 | ||||||||||||||
| MUFG Bank Facility | Maximum | ||||||||||||||||
| Debt Instrument [Line Items] | ||||||||||||||||
| Maximum borrowing capacity | $ 600,000,000 | |||||||||||||||
| HC IV | ||||||||||||||||
| Debt Instrument [Line Items] | ||||||||||||||||
| Debt instrument license description | HC IV received its license to operate as a SBIC on October 27, 2020. The license has a 10-year term. | |||||||||||||||
| License term | 10 years | |||||||||||||||
| Maximum borrowing capacity | $ 175,000,000 | |||||||||||||||
| Regulatory capital commitment amount | $ 87,500,000 | |||||||||||||||
| Outstanding balance | $ 175,000,000.0 | |||||||||||||||
| Investments held by number of companies | investment | 25 | 21 | ||||||||||||||
| Investments at fair value | $ 331,500,000 | $ 343,700,000 | ||||||||||||||
| Percentage of total investment portfolio | 10.20% | 11.60% | ||||||||||||||
| Tangible assets | $ 341,800,000 | $ 348,600,000 | ||||||||||||||
| Percentage of total assets held | 10.00% | 11.50% | ||||||||||||||