Summary of Significant Accounting Policies - Narrative (Details)
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3 Months Ended |
9 Months Ended |
11 Months Ended |
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Mar. 30, 2020
USD ($)
$ / shares
shares
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Sep. 30, 2023
USD ($)
numberOfAgreement
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Sep. 30, 2022
USD ($)
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Sep. 30, 2023
USD ($)
numberOfAgreement
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Sep. 30, 2022
USD ($)
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Dec. 31, 2016
USD ($)
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Dec. 31, 2022
USD ($)
numberOfAgreement
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Feb. 04, 2016
USD ($)
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| Securities Financing Transaction [Line Items] |
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| Number of collateralized agreements | numberOfAgreement |
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1
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1
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1
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| Cost basis of securities purchased under collateralized agreements to resell |
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$ 30,000,000
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$ 30,000,000
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$ 30,000,000
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| Fair value of securities purchased under collateralized agreements to resell |
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16,500,000
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16,500,000
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16,539,000
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| Cash equivalents |
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0
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0
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0
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| Investment income, interest, paid-in-kind |
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7,917,000
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$ 6,193,000
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24,807,000
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$ 21,993,000
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| Investment income, dividend, paid-in-kind |
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$ 6,988,000
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5,995,000
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$ 20,225,000
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16,338,000
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| Investments threshold period past due for nonaccrual status |
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30 days
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30 days
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| Income tax provision (benefit) |
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$ (918,000)
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(43,000)
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$ 335,000
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122,000
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| Current income tax expense (benefit) |
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(627,000)
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(13,000)
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401,000
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(5,000)
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|
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| Deferred income tax provision (benefit) |
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(291,000)
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(30,000)
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(66,000)
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127,000
|
|
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| Deferred tax liability |
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$ 2,790,000
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$ 2,790,000
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$ 8,487,000
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| Dividend reinvestment plan, share price percentage, threshold |
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110.00%
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110.00%
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| Investments in Majority-owned Subsidiaries |
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| Securities Financing Transaction [Line Items] |
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| Shares redeemed for a promissory note (in shares) | shares |
105,030
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| Investments in Majority-owned Subsidiaries | Debt Investments |
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| Securities Financing Transaction [Line Items] |
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| Redemption of shares paid-in-kind |
$ 11,315,000
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| Interest rate |
7.00%
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| Common Stock |
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| Securities Financing Transaction [Line Items] |
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| Stock repurchase program, authorized amount |
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$ 50,000,000
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| Common stock repurchased |
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$ 0
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$ 0
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$ 0
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$ 0
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$ 2,948,000
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| Common Stock | New Mountain Net Lease Corporation |
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| Securities Financing Transaction [Line Items] |
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| Sale of stock, number of shares issued (in shares) | shares |
105,030
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| Sale of stock, price per share (in dollars per share) | $ / shares |
$ 107.73
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| Sale of stock, consideration received |
$ 11,315,000
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