Income Taxes - Components of Accumulated Losses on Tax Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022	Mar. 31, 2022
Income Tax Disclosure [Abstract]
Undistributed ordinary income	$ 59,879	$ 24,468	$ 56,120
Capital loss carryforward	(920,914)	(880,548)	(817,268)
Other temporary book-to-tax differences			(24,678)
Unrealized appreciation (depreciation)	(237,438)	(262,999)	(288,164)
Total accumulated under-distributed (over-distributed) earnings	$ (1,098,473)	$ (1,119,079)	$ (1,073,990)