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Summary of Significant Accounting Policies - Schedule of Properties (Details) - New Mountain Net Lease Corporation ft² in Thousands, $ in Thousands | Sep. 30, 2025 USD ($) ft²
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Property, Plant and Equipment [Line Items] |
Fair value | $ 114,944
NM NL Holdings LP / NM GP Holdco LLC |
Property, Plant and Equipment [Line Items] |
Fair value | $ 106,271
NM YI, LLC |
Property, Plant and Equipment [Line Items] |
Total square feet | ft² | 212
Fair value | $ 8,673

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