Fair Value Measurements - Summary of Quantitative Information of Fair Value Measurements of Investments (Parenthetical) (Detail) - Level 3 [Member]	6 Months Ended	12 Months Ended
	Jun. 30, 2020	Dec. 31, 2019
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Valuation technique	us-gaap:IncomeApproachValuationTechniqueMember
Measurement Input, Discount Rate
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Valuation technique	trilinc:HybridIncomeAndCollateralBasedApproachMember	trilinc:HybridIncomeAndCollateralBasedApproachMember
Other Investments [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Valuation technique	trilinc:HybridIncomeAndCollateralBasedApproachMember	trilinc:HybridIncomeAndCollateralBasedApproachMember
Other Investments [Member] | Measurement Input, Discount Rate
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Additional unobservable inputs	0.20	0.20
Minimum [Member] | Senior Secured Trade Finance Participations [Member] | Income Approach (DCF) [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Expected collection period	2 years	2 years
Minimum [Member] | Senior Secured Trade Finance Participations [Member] | Income Approach (DCF) [Member] | Recovery Rate [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Additional unobservable inputs	0.15	0.15
Maximum [Member] | Senior Secured Trade Finance Participations [Member] | Income Approach (DCF) [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Expected collection period	3 years	3 years
Maximum [Member] | Senior Secured Trade Finance Participations [Member] | Income Approach (DCF) [Member] | Recovery Rate [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Additional unobservable inputs	0.30	0.30