v3.25.2

Financial Highlights (Details) $ / shares in Units, shares in Thousands, $ in Thousands | 3 Months Ended | 9 Months Ended
--- | --- | ---
Jun. 30, 2025 USD ($) $ / shares shares | Jun. 30, 2024 USD ($) $ / shares shares | Jun. 30, 2025 USD ($) $ / shares shares | Jun. 30, 2024 USD ($) $ / shares shares
Investment Company, Financial Highlights [Roll Forward] |  |  |  |
Net asset value per share at beginning of period (in dollars per share) | $ 16.75 | $ 18.72 | $ 18.09 | $ 19.63
Net investment income (in dollars per share) | 0.38 | 0.54 | 1.37 | 1.63
Net unrealized appreciation (depreciation) (in dollars per share) | (0.20) | (0.33) | (0.98) | (0.28)
Net realized gains (losses) (in dollars per share) | (0.15) | (0.85) | (0.28) | (1.06)
(Provision) benefit for taxes on realized and unrealized gains (losses) (in dollars Per share) | 0 | 0 | 0 | (0.01)
Distributions of net investment income to stockholders (dollars per share) | (0.42) | (0.55) | (1.44) | (1.72)
Net asset value per share at end of period (in dollars per share) | 16.76 | 18.19 | 16.76 | 18.19
Per share market value at beginning of period (in dollars per share) | 15.36 | 19.66 | 16.31 | 20.12
Per share market value at end of period (in dollars per share) | $ 13.66 | $ 18.81 | $ 13.66 | $ 18.81
Total return | (8.39%) | (1.51%) | (7.93%) | 2.13%
Common shares outstanding at beginning of period (in shares) | shares | 88,086 | 81,396 | 82,245 | 77,225
Common shares outstanding at end of period (in shares) | shares | 88,086 | 82,245 | 88,086 | 82,245
Net assets at beginning of period | $ | $ 1,475,113 | $ 1,524,099 | $ 1,487,811 | $ 1,515,764
Net assets at end of period | $ | 1,476,469 | 1,496,133 | 1,476,469 | 1,496,133
Average net assets | $ | $ 1,488,823 | $ 1,524,503 | $ 1,487,303 | $ 1,524,180
Ratio of net investment income to average net assets | 9.02% | 11.76% | 10.50% | 11.40%
Ratio of total expenses to average net assets | 12.69% | 14.54% | 12.72% | 14.42%
Ratio of net expenses to average net assets | 11.24% | 13.29% | 10.97% | 13.75%
Ratio of portfolio turnover to average investments at fair value | 4.86% | 5.95% | 25.59% | 23.97%
Weighted average outstanding debt | $ | $ 1,477,143 | $ 1,711,978 | $ 1,595,421 | $ 1,680,876
Average debt per share (dollars per share) | $ 16.77 | $ 20.92 | $ 18.68 | $ 21.06
Asset coverage ratio | 199.86% | 183.36% | 199.86% | 183.36%
Outstanding senior securities | $ | $ 1,466,100 | $ 1,743,400 | $ 1,466,100 | $ 1,743,400

X
- References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form N-2 -Section Item 4 -Subsection 3 -Paragraph 2 + Details
Name: | cef_SeniorSecuritiesAmt
Namespace Prefix: | cef_
Data Type: | xbrli:monetaryItemType
Balance Type: | na
Period Type: | instant

X
- Definition Gain (Loss), Investment and Derivative, Operating, Tax Expense (Benefit) Per Share + References No definition available. + Details
Name: | ocsl_GainLossInvestmentAndDerivativeOperatingTaxExpenseBenefitPerShare
Namespace Prefix: | ocsl_
Data Type: | dtr-types:perShareItemType
Balance Type: | na
Period Type: | duration

X
- Definition Investment Company, Average Long-Term Debt Outstanding Per Share + References No definition available. + Details
Name: | ocsl_InvestmentCompanyAverageLongTermDebtOutstandingPerShare
Namespace Prefix: | ocsl_
Data Type: | dtr-types:perShareItemType
Balance Type: | na
Period Type: | duration

X
- Definition Investment Company, Expense Ratio, Net Expenses + References No definition available. + Details
Name: | ocsl_InvestmentCompanyExpenseRatioNetExpenses
Namespace Prefix: | ocsl_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Investment Company, Expense Ratio, Total Expenses + References No definition available. + Details
Name: | ocsl_InvestmentCompanyExpenseRatioTotalExpenses
Namespace Prefix: | ocsl_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Investment Company, Portfolio Turnover Ratio + References No definition available. + Details
Name: | ocsl_InvestmentCompanyPortfolioTurnoverRatio
Namespace Prefix: | ocsl_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of net assets (liabilities). + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Section 50 -Paragraph 1 -SubTopic 30 -Topic 205 -Publisher FASB -URI https://asc.fasb.org/1943274/2147479910/205-30-50-1 + Details
Name: | us-gaap_AssetsNet
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Number of shares of common stock outstanding. Common stock represent the ownership interest in a corporation. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Section 50 -Paragraph 2 -SubTopic 10 -Topic 505 -Publisher FASB -URI https://asc.fasb.org/1943274/2147481112/505-10-50-2 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 210 -SubTopic 10 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(29)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480566/210-10-S99-1 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Topic 946 -SubTopic 210 -Name Accounting Standards Codification -Section S99 -Paragraph 2 -Subparagraph (SX 210.6-05(4)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147479170/946-210-S99-2 Reference 4: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 946 -SubTopic 220 -Name Accounting Standards Codification -Section S99 -Paragraph 3 -Subparagraph (SX 210.6-09(4)(b)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147479134/946-220-S99-3 Reference 5: http://www.xbrl.org/2003/role/disclosureRef -Topic 946 -SubTopic 210 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.6-04(16)(a)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147479170/946-210-S99-1 Reference 6: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 946 -SubTopic 220 -Name Accounting Standards Codification -Section S99 -Paragraph 3 -Subparagraph (SX 210.6-09(7)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147479134/946-220-S99-3 + Details
Name: | us-gaap_CommonStockSharesOutstanding
Namespace Prefix: | us-gaap_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | instant

X
- Definition Amount of average net assets for investment company. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 946 -SubTopic 205 -Name Accounting Standards Codification -Section 50 -Paragraph 10 -Publisher FASB -URI https://asc.fasb.org/1943274/2147478494/946-205-50-10 Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 946 -SubTopic 205 -Name Accounting Standards Codification -Section 50 -Paragraph 11 -Publisher FASB -URI https://asc.fasb.org/1943274/2147478494/946-205-50-11 + Details
Name: | us-gaap_InvestmentCompanyAverageNetAssets
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Per share or unit amount of distribution to shareholders. Includes, but is not limited to, dividend and capital gain. Excludes distribution for tax return of capital. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 946 -SubTopic 205 -Name Accounting Standards Codification -Section 50 -Paragraph 7 -Subparagraph (e) -Publisher FASB -URI https://asc.fasb.org/1943274/2147478494/946-205-50-7 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 946 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 8 -Publisher FASB -URI https://asc.fasb.org/1943274/2147480990/946-20-50-8 + Details
Name: | us-gaap_InvestmentCompanyDistributionToShareholdersPerShare
Namespace Prefix: | us-gaap_
Data Type: | dtr-types:perShareItemType
Balance Type: | na
Period Type: | duration

X
- Definition A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period. + References No definition available. + Details
Name: | us-gaap_InvestmentCompanyFinancialHighlightsRollForward
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Per-basic-share or unit amount, after investment expense, of dividend and interest investment income (loss) from investment held by investment company. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 946 -SubTopic 205 -Name Accounting Standards Codification -Section 50 -Paragraph 7 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org/1943274/2147478494/946-205-50-7 + Details
Name: | us-gaap_InvestmentCompanyInvestmentIncomeLossPerShare
Namespace Prefix: | us-gaap_
Data Type: | dtr-types:perShareItemType
Balance Type: | na
Period Type: | duration

X
- Definition Percentage of investment income (loss) to average net assets. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 946 -SubTopic 205 -Name Accounting Standards Codification -Section 50 -Paragraph 10 -Publisher FASB -URI https://asc.fasb.org/1943274/2147478494/946-205-50-10 + Details
Name: | us-gaap_InvestmentCompanyInvestmentIncomeLossRatio
Namespace Prefix: | us-gaap_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Market value per share of investment portfolio by investment company. Includes, but is not limited to, per unit, membership interest, or other ownership interest. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 946 -SubTopic 205 -Name Accounting Standards Codification -Section 50 -Paragraph 7 -Publisher FASB -URI https://asc.fasb.org/1943274/2147478494/946-205-50-7 + Details
Name: | us-gaap_InvestmentCompanyMarketValuePerShare
Namespace Prefix: | us-gaap_
Data Type: | dtr-types:perShareItemType
Balance Type: | na
Period Type: | instant

X
- Definition Per-share or unit amount of realized gain (loss) on investment held by investment company. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 946 -SubTopic 205 -Name Accounting Standards Codification -Section 50 -Paragraph 7 -Subparagraph (c) -Publisher FASB -URI https://asc.fasb.org/1943274/2147478494/946-205-50-7 + Details
Name: | us-gaap_InvestmentCompanyRealizedGainLossOnInvestmentPerShare
Namespace Prefix: | us-gaap_
Data Type: | dtr-types:perShareItemType
Balance Type: | na
Period Type: | duration

X
- Definition Percentage of total assets less all liabilities and indebtedness not represented by senior security, to senior security representing indebtedness. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Name Investment Company Act of 1940 -Section 61 -Paragraph a -Subparagraph (1) -Publisher SEC + Details
Name: | us-gaap_InvestmentCompanySeniorSecurityIndebtednessAssetCoverageRatio
Namespace Prefix: | us-gaap_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Percentage increase (decrease) in fund net asset value, assuming reinvestment of dividends and capital gain distributions. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 946 -SubTopic 205 -Name Accounting Standards Codification -Section 50 -Paragraph 27 -Publisher FASB -URI https://asc.fasb.org/1943274/2147478494/946-205-50-27 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 946 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Publisher FASB -URI https://asc.fasb.org/1943274/2147480990/946-20-50-2 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Topic 946 -SubTopic 205 -Name Accounting Standards Codification -Section 50 -Paragraph 18 -Publisher FASB -URI https://asc.fasb.org/1943274/2147478494/946-205-50-18 + Details
Name: | us-gaap_InvestmentCompanyTotalReturn
Namespace Prefix: | us-gaap_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Per-share or unit amount of unrealized gain (loss) on investment held by investment company. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 946 -SubTopic 205 -Name Accounting Standards Codification -Section 50 -Paragraph 7 -Subparagraph (c) -Publisher FASB -URI https://asc.fasb.org/1943274/2147478494/946-205-50-7 + Details
Name: | us-gaap_InvestmentCompanyUnrealizedGainLossOnInvestmentPerShare
Namespace Prefix: | us-gaap_
Data Type: | dtr-types:perShareItemType
Balance Type: | na
Period Type: | duration

X
- Definition Average amount outstanding of long-term debt. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name Regulation S-K (SK) -Number 229 -Section 1402 -Paragraph a -Publisher SEC Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Name Regulation S-K (SK) -Number 229 -Section 1402 -Paragraph b -Subparagraph (1) -Publisher SEC Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Topic 946 -SubTopic 220 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.6-07(3)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147479134/946-220-S99-1 + Details
Name: | us-gaap_LongTermDebtAverageAmountOutstanding
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Net asset value per share or per unit of investments in certain entities that calculate net asset value per share. Includes, but is not limited to, by unit, membership interest, or other ownership interest. Investment includes, but is not limited to, investment in certain hedge funds, venture capital funds, private equity funds, real estate partnerships or funds. Excludes fair value disclosure. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Topic 946 -SubTopic 830 -Name Accounting Standards Codification -Section 55 -Paragraph 12 -Publisher FASB -URI https://asc.fasb.org/1943274/2147479168/946-830-55-12 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 946 -SubTopic 210 -Name Accounting Standards Codification -Section 45 -Paragraph 4 -Publisher FASB -URI https://asc.fasb.org/1943274/2147477796/946-210-45-4 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Topic 946 -SubTopic 205 -Name Accounting Standards Codification -Section 50 -Paragraph 7 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org/1943274/2147478494/946-205-50-7 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Topic 946 -SubTopic 205 -Name Accounting Standards Codification -Section 50 -Paragraph 7 -Subparagraph (h) -Publisher FASB -URI https://asc.fasb.org/1943274/2147478494/946-205-50-7 Reference 5: http://www.xbrl.org/2003/role/disclosureRef -Topic 946 -SubTopic 505 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Publisher FASB -URI https://asc.fasb.org/1943274/2147478448/946-505-50-1 Reference 6: http://www.xbrl.org/2003/role/disclosureRef -Topic 946 -SubTopic 210 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.6-04(19)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147479170/946-210-S99-1 Reference 7: http://www.xbrl.org/2003/role/disclosureRef -Topic 946 -SubTopic 210 -Name Accounting Standards Codification -Section S99 -Paragraph 2 -Subparagraph (SX 210.6-05(4)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147479170/946-210-S99-2 + Details
Name: | us-gaap_NetAssetValuePerShare
Namespace Prefix: | us-gaap_
Data Type: | dtr-types:perShareItemType
Balance Type: | na
Period Type: | instant