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INVESTMENTS - Schedule of Industry Composition of Investment at Fair Value (Details) - USD ($)
$ in Thousands
 9 Months Ended 12 Months Ended
Sep. 30, 2023
Dec. 31, 2022
Schedule of Investments [Line Items]    
Fair Value $ 2,521,635 $ 2,448,935 [1]
Jocassee Partners LLC    
Schedule of Investments [Line Items]    
Fair Value 1,256,876 1,209,063
Sierra JV    
Schedule of Investments [Line Items]    
Fair Value $ 91,902 $ 110,047
Percentage of Total Portfolio, at Fair Value | Industry Concentration Risk    
Schedule of Investments [Line Items]    
Percentage of Total Portfolio 100.00% 100.00%
Percentage of Total Portfolio, at Fair Value | Industry Concentration Risk | Jocassee Partners LLC    
Schedule of Investments [Line Items]    
Percentage of Total Portfolio 100.00% 100.00%
Percentage of Total Portfolio, at Fair Value | Industry Concentration Risk | Sierra JV    
Schedule of Investments [Line Items]    
Percentage of Total Portfolio 100.00% 100.00%
Aerospace and Defense    
Schedule of Investments [Line Items]    
Fair Value $ 132,059 $ 120,945
Aerospace and Defense | Jocassee Partners LLC    
Schedule of Investments [Line Items]    
Fair Value $ 80,321 $ 69,133
Aerospace and Defense | Percentage of Total Portfolio, at Fair Value | Industry Concentration Risk    
Schedule of Investments [Line Items]    
Percentage of Total Portfolio 5.20% 4.90%
Aerospace and Defense | Percentage of Total Portfolio, at Fair Value | Industry Concentration Risk | Jocassee Partners LLC    
Schedule of Investments [Line Items]    
Percentage of Total Portfolio 6.40% 5.70%
Automotive    
Schedule of Investments [Line Items]    
Fair Value $ 82,755 $ 76,934
Automotive | Jocassee Partners LLC    
Schedule of Investments [Line Items]    
Fair Value 23,133 20,625
Automotive | Sierra JV    
Schedule of Investments [Line Items]    
Fair Value $ 2,347 $ 2,283
Automotive | Percentage of Total Portfolio, at Fair Value | Industry Concentration Risk    
Schedule of Investments [Line Items]    
Percentage of Total Portfolio 3.30% 3.20%
Automotive | Percentage of Total Portfolio, at Fair Value | Industry Concentration Risk | Jocassee Partners LLC    
Schedule of Investments [Line Items]    
Percentage of Total Portfolio 1.80% 1.70%
Automotive | Percentage of Total Portfolio, at Fair Value | Industry Concentration Risk | Sierra JV    
Schedule of Investments [Line Items]    
Percentage of Total Portfolio 2.50% 2.10%
Banking, Finance, Insurance and Real Estate    
Schedule of Investments [Line Items]    
Fair Value $ 372,497 $ 312,936
Banking, Finance, Insurance and Real Estate | Jocassee Partners LLC    
Schedule of Investments [Line Items]    
Fair Value 114,941 105,047
Banking, Finance, Insurance and Real Estate | Sierra JV    
Schedule of Investments [Line Items]    
Fair Value $ 677 $ 1,414
Banking, Finance, Insurance and Real Estate | Percentage of Total Portfolio, at Fair Value | Industry Concentration Risk    
Schedule of Investments [Line Items]    
Percentage of Total Portfolio 14.80% 12.80%
Banking, Finance, Insurance and Real Estate | Percentage of Total Portfolio, at Fair Value | Industry Concentration Risk | Jocassee Partners LLC    
Schedule of Investments [Line Items]    
Percentage of Total Portfolio 9.10% 8.70%
Banking, Finance, Insurance and Real Estate | Percentage of Total Portfolio, at Fair Value | Industry Concentration Risk | Sierra JV    
Schedule of Investments [Line Items]    
Percentage of Total Portfolio 0.70% 1.30%
Beverage, Food and Tobacco    
Schedule of Investments [Line Items]    
Fair Value $ 39,573 $ 34,690
Beverage, Food and Tobacco | Jocassee Partners LLC    
Schedule of Investments [Line Items]    
Fair Value 28,953 25,885
Beverage, Food and Tobacco | Sierra JV    
Schedule of Investments [Line Items]    
Fair Value $ 3,302 $ 3,181
Beverage, Food and Tobacco | Percentage of Total Portfolio, at Fair Value | Industry Concentration Risk    
Schedule of Investments [Line Items]    
Percentage of Total Portfolio 1.60% 1.40%
Beverage, Food and Tobacco | Percentage of Total Portfolio, at Fair Value | Industry Concentration Risk | Jocassee Partners LLC    
Schedule of Investments [Line Items]    
Percentage of Total Portfolio 2.30% 2.10%
Beverage, Food and Tobacco | Percentage of Total Portfolio, at Fair Value | Industry Concentration Risk | Sierra JV    
Schedule of Investments [Line Items]    
Percentage of Total Portfolio 3.60% 2.90%
Capital Equipment    
Schedule of Investments [Line Items]    
Fair Value $ 135,679 $ 141,479
Capital Equipment | Jocassee Partners LLC    
Schedule of Investments [Line Items]    
Fair Value 24,955 25,014
Capital Equipment | Sierra JV    
Schedule of Investments [Line Items]    
Fair Value $ 9,250 $ 9,208
Capital Equipment | Percentage of Total Portfolio, at Fair Value | Industry Concentration Risk    
Schedule of Investments [Line Items]    
Percentage of Total Portfolio 5.40% 5.80%
Capital Equipment | Percentage of Total Portfolio, at Fair Value | Industry Concentration Risk | Jocassee Partners LLC    
Schedule of Investments [Line Items]    
Percentage of Total Portfolio 2.00% 2.10%
Capital Equipment | Percentage of Total Portfolio, at Fair Value | Industry Concentration Risk | Sierra JV    
Schedule of Investments [Line Items]    
Percentage of Total Portfolio 10.10% 8.40%
Chemicals, Plastics, and Rubber    
Schedule of Investments [Line Items]    
Fair Value $ 36,720 $ 47,076
Chemicals, Plastics, and Rubber | Jocassee Partners LLC    
Schedule of Investments [Line Items]    
Fair Value 30,817 33,111
Chemicals, Plastics, and Rubber | Sierra JV    
Schedule of Investments [Line Items]    
Fair Value $ 2,954 $ 2,772
Chemicals, Plastics, and Rubber | Percentage of Total Portfolio, at Fair Value | Industry Concentration Risk    
Schedule of Investments [Line Items]    
Percentage of Total Portfolio 1.40% 1.90%
Chemicals, Plastics, and Rubber | Percentage of Total Portfolio, at Fair Value | Industry Concentration Risk | Jocassee Partners LLC    
Schedule of Investments [Line Items]    
Percentage of Total Portfolio 2.50% 2.70%
Chemicals, Plastics, and Rubber | Percentage of Total Portfolio, at Fair Value | Industry Concentration Risk | Sierra JV    
Schedule of Investments [Line Items]    
Percentage of Total Portfolio 3.20% 2.50%
Construction and Building    
Schedule of Investments [Line Items]    
Fair Value $ 30,072 $ 45,049
Construction and Building | Jocassee Partners LLC    
Schedule of Investments [Line Items]    
Fair Value 16,513 17,616
Construction and Building | Sierra JV    
Schedule of Investments [Line Items]    
Fair Value $ 1,872 $ 1,887
Construction and Building | Percentage of Total Portfolio, at Fair Value | Industry Concentration Risk    
Schedule of Investments [Line Items]    
Percentage of Total Portfolio 1.20% 1.80%
Construction and Building | Percentage of Total Portfolio, at Fair Value | Industry Concentration Risk | Jocassee Partners LLC    
Schedule of Investments [Line Items]    
Percentage of Total Portfolio 1.30% 1.50%
Construction and Building | Percentage of Total Portfolio, at Fair Value | Industry Concentration Risk | Sierra JV    
Schedule of Investments [Line Items]    
Percentage of Total Portfolio 2.00% 1.70%
Consumer goods: Durable    
Schedule of Investments [Line Items]    
Fair Value $ 36,567 $ 43,932
Consumer goods: Durable | Jocassee Partners LLC    
Schedule of Investments [Line Items]    
Fair Value 12,915 18,751
Consumer goods: Durable | Sierra JV    
Schedule of Investments [Line Items]    
Fair Value $ 1,005 $ 1,272
Consumer goods: Durable | Percentage of Total Portfolio, at Fair Value | Industry Concentration Risk    
Schedule of Investments [Line Items]    
Percentage of Total Portfolio 1.40% 1.80%
Consumer goods: Durable | Percentage of Total Portfolio, at Fair Value | Industry Concentration Risk | Jocassee Partners LLC    
Schedule of Investments [Line Items]    
Percentage of Total Portfolio 1.00% 1.70%
Consumer goods: Durable | Percentage of Total Portfolio, at Fair Value | Industry Concentration Risk | Sierra JV    
Schedule of Investments [Line Items]    
Percentage of Total Portfolio 1.10% 1.10%
Consumer goods: Non-durable    
Schedule of Investments [Line Items]    
Fair Value $ 27,142 $ 27,693
Consumer goods: Non-durable | Jocassee Partners LLC    
Schedule of Investments [Line Items]    
Fair Value $ 20,874 $ 22,861
Consumer goods: Non-durable | Percentage of Total Portfolio, at Fair Value | Industry Concentration Risk    
Schedule of Investments [Line Items]    
Percentage of Total Portfolio 1.10% 1.10%
Consumer goods: Non-durable | Percentage of Total Portfolio, at Fair Value | Industry Concentration Risk | Jocassee Partners LLC    
Schedule of Investments [Line Items]    
Percentage of Total Portfolio 1.70% 1.90%
Containers, Packaging and Glass    
Schedule of Investments [Line Items]    
Fair Value $ 37,732 $ 37,877
Containers, Packaging and Glass | Jocassee Partners LLC    
Schedule of Investments [Line Items]    
Fair Value 28,684 24,445
Containers, Packaging and Glass | Sierra JV    
Schedule of Investments [Line Items]    
Fair Value $ 0 $ 1,812
Containers, Packaging and Glass | Percentage of Total Portfolio, at Fair Value | Industry Concentration Risk    
Schedule of Investments [Line Items]    
Percentage of Total Portfolio 1.50% 1.50%
Containers, Packaging and Glass | Percentage of Total Portfolio, at Fair Value | Industry Concentration Risk | Jocassee Partners LLC    
Schedule of Investments [Line Items]    
Percentage of Total Portfolio 2.30% 2.00%
Containers, Packaging and Glass | Percentage of Total Portfolio, at Fair Value | Industry Concentration Risk | Sierra JV    
Schedule of Investments [Line Items]    
Percentage of Total Portfolio 0.00% 1.60%
Energy: Electricity    
Schedule of Investments [Line Items]    
Fair Value $ 22,589 $ 7,337
Energy: Electricity | Jocassee Partners LLC    
Schedule of Investments [Line Items]    
Fair Value $ 15,325 $ 15,375
Energy: Electricity | Percentage of Total Portfolio, at Fair Value | Industry Concentration Risk    
Schedule of Investments [Line Items]    
Percentage of Total Portfolio 0.90% 0.30%
Energy: Electricity | Percentage of Total Portfolio, at Fair Value | Industry Concentration Risk | Jocassee Partners LLC    
Schedule of Investments [Line Items]    
Percentage of Total Portfolio 1.20% 1.30%
Energy: Oil and Gas    
Schedule of Investments [Line Items]    
Fair Value $ 4,544 $ 4,776
Energy: Oil and Gas | Jocassee Partners LLC    
Schedule of Investments [Line Items]    
Fair Value $ 6,392 $ 5,726
Energy: Oil and Gas | Percentage of Total Portfolio, at Fair Value | Industry Concentration Risk    
Schedule of Investments [Line Items]    
Percentage of Total Portfolio 0.20% 0.20%
Energy: Oil and Gas | Percentage of Total Portfolio, at Fair Value | Industry Concentration Risk | Jocassee Partners LLC    
Schedule of Investments [Line Items]    
Percentage of Total Portfolio 0.50% 0.50%
Environmental Industries    
Schedule of Investments [Line Items]    
Fair Value $ 53,387 $ 51,006
Environmental Industries | Jocassee Partners LLC    
Schedule of Investments [Line Items]    
Fair Value 6,866 7,314
Environmental Industries | Sierra JV    
Schedule of Investments [Line Items]    
Fair Value $ 8,083 $ 7,797
Environmental Industries | Percentage of Total Portfolio, at Fair Value | Industry Concentration Risk    
Schedule of Investments [Line Items]    
Percentage of Total Portfolio 2.10% 2.10%
Environmental Industries | Percentage of Total Portfolio, at Fair Value | Industry Concentration Risk | Jocassee Partners LLC    
Schedule of Investments [Line Items]    
Percentage of Total Portfolio 0.60% 0.60%
Environmental Industries | Percentage of Total Portfolio, at Fair Value | Industry Concentration Risk | Sierra JV    
Schedule of Investments [Line Items]    
Percentage of Total Portfolio 8.80% 7.10%
Forest Products & Paper | Jocassee Partners LLC    
Schedule of Investments [Line Items]    
Fair Value $ 3,059 $ 2,269
Forest Products & Paper | Percentage of Total Portfolio, at Fair Value | Industry Concentration Risk | Jocassee Partners LLC    
Schedule of Investments [Line Items]    
Percentage of Total Portfolio 0.20% 0.20%
Healthcare and Pharmaceuticals    
Schedule of Investments [Line Items]    
Fair Value $ 201,815 $ 203,576
Healthcare and Pharmaceuticals | Jocassee Partners LLC    
Schedule of Investments [Line Items]    
Fair Value 142,345 128,983
Healthcare and Pharmaceuticals | Sierra JV    
Schedule of Investments [Line Items]    
Fair Value $ 13,407 $ 13,614
Healthcare and Pharmaceuticals | Percentage of Total Portfolio, at Fair Value | Industry Concentration Risk    
Schedule of Investments [Line Items]    
Percentage of Total Portfolio 8.00% 8.30%
Healthcare and Pharmaceuticals | Percentage of Total Portfolio, at Fair Value | Industry Concentration Risk | Jocassee Partners LLC    
Schedule of Investments [Line Items]    
Percentage of Total Portfolio 11.30% 10.70%
Healthcare and Pharmaceuticals | Percentage of Total Portfolio, at Fair Value | Industry Concentration Risk | Sierra JV    
Schedule of Investments [Line Items]    
Percentage of Total Portfolio 14.60% 12.40%
High Tech Industries    
Schedule of Investments [Line Items]    
Fair Value $ 298,811 $ 300,980
High Tech Industries | Jocassee Partners LLC    
Schedule of Investments [Line Items]    
Fair Value 163,461 141,906
High Tech Industries | Sierra JV    
Schedule of Investments [Line Items]    
Fair Value $ 14,156 $ 13,713
High Tech Industries | Percentage of Total Portfolio, at Fair Value | Industry Concentration Risk    
Schedule of Investments [Line Items]    
Percentage of Total Portfolio 11.90% 12.30%
High Tech Industries | Percentage of Total Portfolio, at Fair Value | Industry Concentration Risk | Jocassee Partners LLC    
Schedule of Investments [Line Items]    
Percentage of Total Portfolio 13.00% 11.70%
High Tech Industries | Percentage of Total Portfolio, at Fair Value | Industry Concentration Risk | Sierra JV    
Schedule of Investments [Line Items]    
Percentage of Total Portfolio 15.40% 12.50%
Hotel, Gaming and Leisure    
Schedule of Investments [Line Items]    
Fair Value $ 54,301 $ 54,023
Hotel, Gaming and Leisure | Jocassee Partners LLC    
Schedule of Investments [Line Items]    
Fair Value $ 22,185 $ 23,587
Hotel, Gaming and Leisure | Percentage of Total Portfolio, at Fair Value | Industry Concentration Risk    
Schedule of Investments [Line Items]    
Percentage of Total Portfolio 2.20% 2.20%
Hotel, Gaming and Leisure | Percentage of Total Portfolio, at Fair Value | Industry Concentration Risk | Jocassee Partners LLC    
Schedule of Investments [Line Items]    
Percentage of Total Portfolio 1.80% 2.00%
Investment Funds and Vehicles    
Schedule of Investments [Line Items]    
Fair Value $ 116,646 $ 130,427
Investment Funds and Vehicles | Jocassee Partners LLC    
Schedule of Investments [Line Items]    
Fair Value $ 37,001 $ 61,028
Investment Funds and Vehicles | Percentage of Total Portfolio, at Fair Value | Industry Concentration Risk    
Schedule of Investments [Line Items]    
Percentage of Total Portfolio 4.50% 5.30%
Investment Funds and Vehicles | Percentage of Total Portfolio, at Fair Value | Industry Concentration Risk | Jocassee Partners LLC    
Schedule of Investments [Line Items]    
Percentage of Total Portfolio 3.00% 5.00%
Media: Advertising, Printing and Publishing    
Schedule of Investments [Line Items]    
Fair Value $ 44,811 $ 55,477
Media: Advertising, Printing and Publishing | Jocassee Partners LLC    
Schedule of Investments [Line Items]    
Fair Value 15,482 5,969
Media: Advertising, Printing and Publishing | Sierra JV    
Schedule of Investments [Line Items]    
Fair Value $ 0 $ 10,032
Media: Advertising, Printing and Publishing | Percentage of Total Portfolio, at Fair Value | Industry Concentration Risk    
Schedule of Investments [Line Items]    
Percentage of Total Portfolio 1.80% 2.30%
Media: Advertising, Printing and Publishing | Percentage of Total Portfolio, at Fair Value | Industry Concentration Risk | Jocassee Partners LLC    
Schedule of Investments [Line Items]    
Percentage of Total Portfolio 1.20% 0.50%
Media: Advertising, Printing and Publishing | Percentage of Total Portfolio, at Fair Value | Industry Concentration Risk | Sierra JV    
Schedule of Investments [Line Items]    
Percentage of Total Portfolio 0.00% 9.10%
Media: Broadcasting and Subscription    
Schedule of Investments [Line Items]    
Fair Value $ 20,480 $ 20,257
Media: Broadcasting and Subscription | Jocassee Partners LLC    
Schedule of Investments [Line Items]    
Fair Value $ 32,690 $ 34,676
Media: Broadcasting and Subscription | Percentage of Total Portfolio, at Fair Value | Industry Concentration Risk    
Schedule of Investments [Line Items]    
Percentage of Total Portfolio 0.80% 0.80%
Media: Broadcasting and Subscription | Percentage of Total Portfolio, at Fair Value | Industry Concentration Risk | Jocassee Partners LLC    
Schedule of Investments [Line Items]    
Percentage of Total Portfolio 2.60% 2.90%
Media: Diversified and Production    
Schedule of Investments [Line Items]    
Fair Value $ 67,829 $ 60,561
Media: Diversified and Production | Jocassee Partners LLC    
Schedule of Investments [Line Items]    
Fair Value 28,105 28,897
Media: Diversified and Production | Sierra JV    
Schedule of Investments [Line Items]    
Fair Value $ 3,234 $ 5,498
Media: Diversified and Production | Percentage of Total Portfolio, at Fair Value | Industry Concentration Risk    
Schedule of Investments [Line Items]    
Percentage of Total Portfolio 2.70% 2.50%
Media: Diversified and Production | Percentage of Total Portfolio, at Fair Value | Industry Concentration Risk | Jocassee Partners LLC    
Schedule of Investments [Line Items]    
Percentage of Total Portfolio 2.20% 2.40%
Media: Diversified and Production | Percentage of Total Portfolio, at Fair Value | Industry Concentration Risk | Sierra JV    
Schedule of Investments [Line Items]    
Percentage of Total Portfolio 3.50% 5.00%
Metals and Mining    
Schedule of Investments [Line Items]    
Fair Value $ 32,000 $ 33,125
Metals and Mining | Jocassee Partners LLC    
Schedule of Investments [Line Items]    
Fair Value $ 3,863 $ 5,069
Metals and Mining | Percentage of Total Portfolio, at Fair Value | Industry Concentration Risk    
Schedule of Investments [Line Items]    
Percentage of Total Portfolio 1.30% 1.40%
Metals and Mining | Percentage of Total Portfolio, at Fair Value | Industry Concentration Risk | Jocassee Partners LLC    
Schedule of Investments [Line Items]    
Percentage of Total Portfolio 0.30% 0.40%
Retail | Jocassee Partners LLC    
Schedule of Investments [Line Items]    
Fair Value $ 12,395 $ 15,720
Retail | Sierra JV    
Schedule of Investments [Line Items]    
Fair Value $ 6,028 $ 5,489
Retail | Percentage of Total Portfolio, at Fair Value | Industry Concentration Risk | Jocassee Partners LLC    
Schedule of Investments [Line Items]    
Percentage of Total Portfolio 1.00% 1.30%
Retail | Percentage of Total Portfolio, at Fair Value | Industry Concentration Risk | Sierra JV    
Schedule of Investments [Line Items]    
Percentage of Total Portfolio 6.60% 5.00%
Services: Business    
Schedule of Investments [Line Items]    
Fair Value $ 352,052 $ 338,417
Services: Business | Jocassee Partners LLC    
Schedule of Investments [Line Items]    
Fair Value 208,216 199,805
Services: Business | Sierra JV    
Schedule of Investments [Line Items]    
Fair Value $ 6,870 $ 10,876
Services: Business | Percentage of Total Portfolio, at Fair Value | Industry Concentration Risk    
Schedule of Investments [Line Items]    
Percentage of Total Portfolio 14.00% 13.80%
Services: Business | Percentage of Total Portfolio, at Fair Value | Industry Concentration Risk | Jocassee Partners LLC    
Schedule of Investments [Line Items]    
Percentage of Total Portfolio 16.60% 16.50%
Services: Business | Percentage of Total Portfolio, at Fair Value | Industry Concentration Risk | Sierra JV    
Schedule of Investments [Line Items]    
Percentage of Total Portfolio 7.50% 9.90%
Services: Consumer    
Schedule of Investments [Line Items]    
Fair Value $ 57,578 $ 67,070
Services: Consumer | Jocassee Partners LLC    
Schedule of Investments [Line Items]    
Fair Value 56,439 52,543
Services: Consumer | Sierra JV    
Schedule of Investments [Line Items]    
Fair Value $ 8,449 $ 8,265
Services: Consumer | Percentage of Total Portfolio, at Fair Value | Industry Concentration Risk    
Schedule of Investments [Line Items]    
Percentage of Total Portfolio 2.30% 2.70%
Services: Consumer | Percentage of Total Portfolio, at Fair Value | Industry Concentration Risk | Jocassee Partners LLC    
Schedule of Investments [Line Items]    
Percentage of Total Portfolio 4.50% 4.30%
Services: Consumer | Percentage of Total Portfolio, at Fair Value | Industry Concentration Risk | Sierra JV    
Schedule of Investments [Line Items]    
Percentage of Total Portfolio 9.20% 7.50%
Structured products    
Schedule of Investments [Line Items]    
Fair Value $ 100,827 $ 86,703
Structured products | Percentage of Total Portfolio, at Fair Value | Industry Concentration Risk    
Schedule of Investments [Line Items]    
Percentage of Total Portfolio 4.00% 3.50%
Telecommunications    
Schedule of Investments [Line Items]    
Fair Value $ 26,432 $ 24,058
Telecommunications | Jocassee Partners LLC    
Schedule of Investments [Line Items]    
Fair Value $ 35,066 $ 38,034
Telecommunications | Percentage of Total Portfolio, at Fair Value | Industry Concentration Risk    
Schedule of Investments [Line Items]    
Percentage of Total Portfolio 1.00% 1.00%
Telecommunications | Percentage of Total Portfolio, at Fair Value | Industry Concentration Risk | Jocassee Partners LLC    
Schedule of Investments [Line Items]    
Percentage of Total Portfolio 2.80% 3.10%
Transportation: Cargo    
Schedule of Investments [Line Items]    
Fair Value $ 98,385 $ 89,398
Transportation: Cargo | Jocassee Partners LLC    
Schedule of Investments [Line Items]    
Fair Value 59,279 56,018
Transportation: Cargo | Sierra JV    
Schedule of Investments [Line Items]    
Fair Value $ 6,301 $ 6,221
Transportation: Cargo | Percentage of Total Portfolio, at Fair Value | Industry Concentration Risk    
Schedule of Investments [Line Items]    
Percentage of Total Portfolio 3.90% 3.70%
Transportation: Cargo | Percentage of Total Portfolio, at Fair Value | Industry Concentration Risk | Jocassee Partners LLC    
Schedule of Investments [Line Items]    
Percentage of Total Portfolio 4.70% 4.60%
Transportation: Cargo | Percentage of Total Portfolio, at Fair Value | Industry Concentration Risk | Sierra JV    
Schedule of Investments [Line Items]    
Percentage of Total Portfolio 6.90% 5.60%
Transportation: Consumer    
Schedule of Investments [Line Items]    
Fair Value $ 11,102 $ 11,062
Transportation: Consumer | Jocassee Partners LLC    
Schedule of Investments [Line Items]    
Fair Value 12,626 12,562
Transportation: Consumer | Sierra JV    
Schedule of Investments [Line Items]    
Fair Value $ 3,967 $ 4,713
Transportation: Consumer | Percentage of Total Portfolio, at Fair Value | Industry Concentration Risk    
Schedule of Investments [Line Items]    
Percentage of Total Portfolio 0.40% 0.50%
Transportation: Consumer | Percentage of Total Portfolio, at Fair Value | Industry Concentration Risk | Jocassee Partners LLC    
Schedule of Investments [Line Items]    
Percentage of Total Portfolio 1.00% 1.00%
Transportation: Consumer | Percentage of Total Portfolio, at Fair Value | Industry Concentration Risk | Sierra JV    
Schedule of Investments [Line Items]    
Percentage of Total Portfolio 4.30% 4.30%
Utilities: Electric    
Schedule of Investments [Line Items]    
Fair Value $ 22,584 $ 17,374
Utilities: Electric | Jocassee Partners LLC    
Schedule of Investments [Line Items]    
Fair Value $ 7,120 $ 4,194
Utilities: Electric | Percentage of Total Portfolio, at Fair Value | Industry Concentration Risk    
Schedule of Investments [Line Items]    
Percentage of Total Portfolio 0.90% 0.70%
Utilities: Electric | Percentage of Total Portfolio, at Fair Value | Industry Concentration Risk | Jocassee Partners LLC    
Schedule of Investments [Line Items]    
Percentage of Total Portfolio 0.60% 0.30%
Utilities: Oil and Gas    
Schedule of Investments [Line Items]    
Fair Value $ 4,666 $ 4,697
Utilities: Oil and Gas | Jocassee Partners LLC    
Schedule of Investments [Line Items]    
Fair Value $ 6,855 $ 6,900
Utilities: Oil and Gas | Percentage of Total Portfolio, at Fair Value | Industry Concentration Risk    
Schedule of Investments [Line Items]    
Percentage of Total Portfolio 0.20% 0.20%
Utilities: Oil and Gas | Percentage of Total Portfolio, at Fair Value | Industry Concentration Risk | Jocassee Partners LLC    
Schedule of Investments [Line Items]    
Percentage of Total Portfolio 0.50% 0.60%
[1] All of the investment is or will be encumbered as security for the Company's $1.1 billion senior secured credit facility with ING Capital LLC initially entered into in the February 2019 Credit Facility.