Selected Quarterly Financial Data (Unaudited) - Schedule of Selected Quarterly Financial Data (Details) - USD ($)	3 Months Ended												9 Months Ended			12 Months Ended
	Dec. 31, 2023	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Dec. 31, 2022	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Dec. 31, 2021	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2023	Dec. 31, 2022		Dec. 31, 2023		Mar. 31, 2022		Mar. 31, 2021		Mar. 31, 2020
Quarterly Financial Information Disclosure [Abstract]
Investment Income, Total	$ 71,952,000	$ 68,175,000	$ 68,617,000	$ 67,778,000	$ 63,320,000	$ 58,885,000	$ 53,404,000	$ 54,741,000	$ 54,972,000	$ 52,889,000	$ 50,553,000	$ 50,825,000	$ 208,744,000	$ 175,609,000		$ 276,522,000		$ 213,155,000
Investment Income, Per Share	$ 1.1	$ 1.04	$ 1.05	$ 1.04	$ 0.97	$ 0.91	$ 0.84	$ 0.86	$ 0.86	$ 0.81	$ 0.78	$ 0.78
Net Investment Income, Total	$ 29,769,000	$ 27,896,000	$ 28,850,000	$ 29,484,000	$ 28,013,000	$ 22,637,000	$ 23,493,000	$ 26,889,000	$ 22,496,000	$ 21,231,000	$ 25,345,000	$ 25,635,000	86,516,000	$ 74,143,000		$ 115,999,000		$ 95,961,000
Net Investment Income, Per Share	$ 0.46	$ 0.43	$ 0.44	$ 0.45	$ 0.43	$ 0.35	$ 0.37	$ 0.42	$ 0.35	$ 0.33	$ 0.39	$ 0.39		$ 1.15	[1]	$ 1.78	[1]	$ 1.49	[1]	$ 1.69	[1]	$ 2.16	[1]
Net Realized And Change in Unrealized Gains (Losses), Total	$ 3,492,000	$ 2,067,000	$ (3,447,000)	$ 649,000	$ (26,725,000)	$ (6,644,000)	$ (17,834,000)	$ (22,650,000)	$ (1,956,000)	$ 4,210,000	$ 6,799,000	$ 16,777,000	2,112,000	$ (51,203,000)		$ 2,761,000		$ (13,597,000)
Net Realized And Change in Unrealized Gains (Losses), Per Share	$ 0.05	$ 0.03	$ (0.05)	$ 0.01	$ (0.41)	$ (0.1)	$ (0.28)	$ (0.36)	$ (0.03)	$ 0.06	$ 0.1	$ 0.26		$ (0.79)	[1]	$ 0.04	[1]	$ (0.21)	[1]	0.03	[1]	(3.89)	[1]
Net Income (Loss)	$ 33,262,000	$ 29,963,000	$ 25,404,000	$ 30,132,000	$ 1,288,000	$ 15,993,000	$ 5,659,000	$ 4,239,000	$ 20,540,000	$ 25,441,000	$ 32,144,000	$ 42,411,000	$ 88,628,000	$ 22,940,000		$ 118,760,000		$ 82,364,000
Net Increase (Decrease) in Net Assets from Operations - Basic, Per Share	$ 0.51	$ 0.46	$ 0.39	$ 0.46	$ 0.02	$ 0.25	$ 0.09	$ 0.07	$ 0.32	$ 0.39	$ 0.49	$ 0.65		$ 0.36		$ 1.82		$ 1.28		$ 1.71		$ (1.73)

[1] Financial highlights are based on the weighted average number of shares outstanding for the period presented.