Consolidated Balance Sheets (Parenthetical) - USD ($) |
Sep. 30, 2022 |
Dec. 31, 2021 |
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|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Investment, cost | $ 3,689,627,000 | $ 3,259,246,000 | [1],[2],[3] | |||||||||||||||
| Deferred financing costs, accumulated amortization | $ 10,203,000 | $ 9,462,000 | ||||||||||||||||
| Common stock, par value (in dollars per share) | $ 0.01 | $ 0.01 | ||||||||||||||||
| Common stock, shares authorized (in shares) | 150,000,000 | 150,000,000 | ||||||||||||||||
| Common stock, shares outstanding (in shares) | 76,155,807 | 70,700,885 | ||||||||||||||||
| Common stock, shares issued (in shares) | 76,155,807 | 70,700,885 | ||||||||||||||||
| 3.00% Notes due 2026 | ||||||||||||||||||
| Debt instrument, interest rate, stated percentage | 3.00% | |||||||||||||||||
| 3.00% Notes due 2026 | Unsecured Notes | ||||||||||||||||||
| Debt instrument, interest rate, stated percentage | 3.00% | 3.00% | ||||||||||||||||
| Debt instrument, par value | $ 500,000,000 | $ 500,000,000 | ||||||||||||||||
| 5.20% Notes due 2024 | Unsecured Notes | ||||||||||||||||||
| Debt instrument, interest rate, stated percentage | 5.20% | 5.20% | ||||||||||||||||
| Debt instrument, par value | $ 450,000,000 | $ 450,000,000 | ||||||||||||||||
| SBIC Debentures | Unsecured Notes | ||||||||||||||||||
| Debt instrument, par value | 350,000,000 | 350,000,000 | ||||||||||||||||
| Debt, due within one year | $ 16,000,000 | $ 16,000,000 | ||||||||||||||||
| 4.50% Notes due 2022 | Unsecured Notes | ||||||||||||||||||
| Debt instrument, interest rate, stated percentage | 4.50% | 4.50% | ||||||||||||||||
| Debt instrument, par value | $ 185,000,000 | $ 185,000,000 | ||||||||||||||||
| Control investments | ||||||||||||||||||
| Investment, cost | [4] | 1,199,446,000 | [5] | 1,107,597,000 | [3] | |||||||||||||
| Affiliate investments | ||||||||||||||||||
| Investment, cost | 576,047,000 | [5] | 578,539,000 | [3],[6] | ||||||||||||||
| Non‑Control/Non‑Affiliate investments | ||||||||||||||||||
| Investment, cost | $ 1,914,134,000 | $ 1,573,110,000 | [3],[7] | |||||||||||||||
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