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Related Party Transactions - Additional Information (Details) $ in Thousands			3 Months Ended		9 Months Ended		12 Months Ended
	Jan. 21, 2026 USD ($)	Dec. 05, 2022 USD ($) BusinessDays	Sep. 30, 2026 USD ($)	Sep. 30, 2025 USD ($)	Sep. 30, 2026 USD ($)	Sep. 30, 2025 USD ($)	Dec. 31, 2025 USD ($)	Sep. 21, 2026 USD ($)	Sep. 24, 2025 USD ($)
Related Party Transaction [Line Items]
Percentage of capital contribution invested in joint venture debt notes		70.00%
Percentage of capital contribution invested in joint venture common equity		30.00%
Percentage of principal amount of loan or equipment financing advance		100
Percentage of fee for loan and advance		50.00%
Loan or advance fee payable number of days \| BusinessDays		2
Remaining percentage of fee for loan or advance		50.00%
Percentage of daily average aggregate value of outstanding loans and equipment financings		75
Net proceeds for the sale of investments			$ 52,800		$ 97,500		$ 110,600
Realized gain			(7,472)	$ (20,025)	(18,176)	$ (30,441)
Outstanding payable			$ 49,761		$ 49,761		51,742
8.5% Notes
Related Party Transaction [Line Items]
Debt instrument percentage		8.50%
i 40 LLC
Related Party Transaction [Line Items]
Capital contributions		$ 21,400
JV Partner
Related Party Transaction [Line Items]
Capital contributions		$ 150,000
Joint venture ownership percentage			87.50%		87.50%
Senior Credit Corp 2022 LLC
Related Party Transaction [Line Items]
Joint venture ownership percentage			12.50%		12.50%
Trinity Investor J V I L L C
Related Party Transaction [Line Items]
Capital contributions			$ 18,400		$ 18,400		18,400
Total Investments at fair value			236,200		236,200		225,800
Unfunded capital commitment					3,000		3,000
Trinity Investor J V I L L C \| Debt
Related Party Transaction [Line Items]
Total Investments at fair value			12,900		12,900		12,900
Trinity Investor J V I L L C \| Equity
Related Party Transaction [Line Items]
Total Investments at fair value			5,500		5,500		5,500
Corporate Joint Venture
Related Party Transaction [Line Items]
Outstanding payable			200		200		5,900
Corporate Joint Venture \| Location, Statement of Income, Balance [Axis]: trin:InvestmentFeeAndOtherIncome
Related Party Transaction [Line Items]
Origination and administrative agent fees			900	$ 700	2,100	$ 2,000
Direct Lending 2025 LLC
Related Party Transaction [Line Items]
Capital contributions			23,300		23,300		22,400		$ 100,000
Joint venture ownership percentage									50.00%
Total Investments at fair value			25,900		25,900		30,100
Unfunded capital commitment					87,400		85,100
Net proceeds for the sale of investments			$ 2,000		11,800		48,000
Return of capital					$ 10,600		7,500
EPT 16 LLC
Related Party Transaction [Line Items]
Joint venture ownership percentage			16.30%		16.30%
Total Investments at fair value			$ 145,500		$ 145,500		123,100
Net proceeds for the sale of investments			21,600		49,900		74,000
Other receivables			100		100
Outstanding payable							1,400
EPT 16 LLC \| Maximum
Related Party Transaction [Line Items]
Other receivables							$ 200
New JV Partner
Related Party Transaction [Line Items]
Capital contributions	$ 50,000
Unfunded capital commitment					21,500
Joint venture agreement date	Jan. 21, 2026
SBIC LP
Related Party Transaction [Line Items]
Total Investments at fair value			36,100		36,100
SBIC co-invested amount			29,200		36,200
Other receivables			100		100
Limited partnership interest			5,000		5,000
Unfunded Limited Partnership Interest			3,800		3,800
SBIC LP \| Limited Partner
Related Party Transaction [Line Items]
Capital contributions			5,000		5,000
CapTrin Partners, LLC
Related Party Transaction [Line Items]
Other receivables			500		500
Desert Star JV Partner
Related Party Transaction [Line Items]
Capital contributions								$ 25,000
Joint venture ownership percentage								12.50%
Desert Star 2026 LLC
Related Party Transaction [Line Items]
Capital contributions			56,000		56,000			$ 175,000
Joint venture ownership percentage								87.50%
Total Investments at fair value			128,200		128,200
Unfunded capital commitment					119,000
Net proceeds for the sale of investments			130,000		130,000
Desert Star 2026 LLC \| Location, Statement of Income, Balance [Axis]: us-gaap:RealizedInvestmentGainsLosses
Related Party Transaction [Line Items]
Realized gain			800		800
Desert Star 2026 LLC \| Location, Statement of Income, Balance [Axis]: trin:InvestmentFeeAndOtherIncome
Related Party Transaction [Line Items]
Origination fees			$ 600		$ 600