Statements of Assets, Liabilities and Members' Capital (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2025		Dec. 31, 2024
Statement of Financial Position [Abstract]
Investments, cost	$ 389,132	[1]	$ 375,695	[2]
Deferred financing costs, accumulated amortization	$ 416		$ 334
Common units, issued (in shares)	33,306,325		33,306,325
Common units, outstanding (in shares)	33,306,325		33,306,325

[1] New Mountain Guardian IV Income Fund, L.L.C. (the "Company") generally acquires its investments in private transactions exempt from registration under the Securities Act of 1933, as amended (the "Securities Act"). These investments are generally subject to certain limitations on resale, and may be deemed to be "restricted securities" under the Securities Act.

[2] New Mountain Guardian IV Income Fund, L.L.C. (the "Company") generally acquires its investments in private transactions exempt from registration under the Securities Act of 1933, as amended (the "Securities Act"). These investments are generally subject to certain limitations on resale, and may be deemed to be "restricted securities" under the Securities Act.