Investments - Summary of Operating and Balance Sheet Data (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024	Jun. 30, 2025	Dec. 31, 2024	Jun. 30, 2024	Dec. 31, 2023
Income Statement [Abstract]
Expenses	$ (17,373)	$ (11,679)	$ (47,075)	$ (34,125)
Income tax benefit (expense)	(3,525)	(1,315)	(8,585)	(2,577)
Net increase in net assets resulting from operations	34,809	23,176	99,280	68,365
Balance Sheet Related Disclosures [Abstract]
Stockholders’ equity	1,371,087	1,163,920	1,371,087	1,163,920	$ 1,319,892	$ 1,231,208	$ 1,096,309	$ 979,349
Clarion Safety Systems, LLC
Income Statement [Abstract]
Revenues	8,499	4,063	23,777	12,620
Expenses	(6,841)	(3,710)	(20,330)	(10,816)
Income (loss) before taxes	1,658	353	3,447	1,804
Income tax benefit (expense)	(454)	(98)	(945)	(503)
Net increase in net assets resulting from operations	1,204	255	2,502	1,301
Balance Sheet Related Disclosures [Abstract]
Current assets	14,094		14,094			7,124
Non-current assets	83,202		83,202			74,214
Current liabilities	2,571		2,571			2,551
Non-current liabilities	22,895		22,895			22,680
Stockholders’ equity	$ 71,830		$ 71,830			$ 56,107
Ownership percentage	95.00%		95.00%			96.00%
Sill Holdings, LLC
Income Statement [Abstract]
Revenues	$ 8,031	6,391	$ 29,876	14,636
Expenses	(7,922)	(5,846)	(25,571)	(15,515)
Income (loss) before taxes	109	545	4,305	(879)
Income tax benefit (expense)	375	(1,718)	(327)	(1,038)
Net increase in net assets resulting from operations	484	$ (1,173)	3,978	$ (1,917)
Balance Sheet Related Disclosures [Abstract]
Current assets	12,086		12,086			$ 12,039
Non-current assets	106,032		106,032			107,938
Current liabilities	3,957		3,957			5,585
Non-current liabilities	19,255		19,255			18,908
Stockholders’ equity	$ 94,906		$ 94,906			$ 95,484
Ownership percentage	93.00%		93.00%			93.00%