Investments - Summary of Operating and Balance Sheet Data (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Investment Company, Financial Highlights [Line Items]
Expenses	$ (17,916,954)	$ (10,261,852)
Income tax expense	(3,240,304)	(266,789)
Net increase in net assets resulting from operations	42,985,490	30,046,363
Lawn Doctor
Investment Company, Financial Highlights [Line Items]
Revenues	35,018,000	28,677,000
Expenses	(31,749,000)	(27,232,000)
Income (loss) before taxes	3,269,000	1,445,000
Income tax expense	(832,000)	(371,000)
Consolidated net income (loss)	2,437,000	1,074,000
Net loss attributable to non-controlling interests	107,000	213,000
Net increase in net assets resulting from operations	2,544,000	1,287,000
Current assets	13,926,000	8,386,000
Non-current assets	92,309,000	94,601,000
Current liabilities	7,961,000	7,670,000
Non-current liabilities	63,576,000	53,386,000
Non-controlling interest	(500,000)	(393,000)
Stockholders’ equity	$ 35,198,000	$ 42,324,000
Ownership percentage	61.00%	61.00%
Polyform
Investment Company, Financial Highlights [Line Items]
Revenues	$ 22,297,000	$ 18,981,000
Expenses	(20,097,000)	(17,372,000)
Income (loss) before taxes	2,200,000	1,609,000
Income tax expense	(574,000)	(469,000)
Consolidated net income (loss)	1,626,000	1,140,000
Net loss attributable to non-controlling interests	0	0
Net increase in net assets resulting from operations	1,626,000	1,140,000
Current assets	9,940,000	9,692,000
Non-current assets	28,948,000	30,033,000
Current liabilities	2,290,000	2,461,000
Non-current liabilities	21,557,000	21,563,000
Non-controlling interest	0	0
Stockholders’ equity	$ 15,041,000	$ 15,701,000
Ownership percentage	87.00%	87.00%
Roundtables
Investment Company, Financial Highlights [Line Items]
Revenues	$ 13,128,000	$ 10,942,000
Expenses	(13,276,000)	(11,692,000)
Income (loss) before taxes	(148,000)	(750,000)
Income tax expense	(469,000)	1,443,000
Consolidated net income (loss)	(617,000)	693,000
Net loss attributable to non-controlling interests	0	0
Net increase in net assets resulting from operations	(617,000)	693,000
Current assets	2,043,000	4,167,000
Non-current assets	61,955,000	59,582,000
Current liabilities	4,738,000	4,407,000
Non-current liabilities	19,771,000	19,553,000
Non-controlling interest	0	0
Stockholders’ equity	$ 39,489,000	$ 39,789,000
Ownership percentage	81.00%	81.00%
HSH
Investment Company, Financial Highlights [Line Items]
Revenues	$ 32,918,000	$ 13,940,000
Expenses	(30,769,000)	(15,633,000)
Income (loss) before taxes	2,149,000	(1,693,000)
Income tax expense	(456,000)	109,000
Consolidated net income (loss)	1,693,000	(1,584,000)
Net loss attributable to non-controlling interests	0	0
Net increase in net assets resulting from operations	1,693,000	(1,584,000)
Current assets	14,260,000	12,684,000
Non-current assets	39,653,000	42,701,000
Current liabilities	7,341,000	5,733,000
Non-current liabilities	28,536,000	29,297,000
Non-controlling interest	0	0
Stockholders’ equity	$ 18,036,000	$ 20,355,000
Ownership percentage	75.00%	75.00%
ATA
Investment Company, Financial Highlights [Line Items]
Revenues	$ 59,021,000
Expenses	(52,494,000)
Income (loss) before taxes	6,527,000
Income tax expense	0
Consolidated net income (loss)	6,527,000
Net loss attributable to non-controlling interests	0
Net increase in net assets resulting from operations	6,527,000
Current assets	10,029,000
Non-current assets	90,510,000
Current liabilities	9,002,000
Non-current liabilities	43,458,000
Non-controlling interest	0
Stockholders’ equity	$ 48,079,000
Ownership percentage	75.00%
Douglas
Investment Company, Financial Highlights [Line Items]
Revenues	$ 6,099,000
Expenses	(19,146,000)
Income (loss) before taxes	(13,047,000)
Income tax expense	2,608,000
Consolidated net income (loss)	(10,439,000)
Net loss attributable to non-controlling interests	0
Net increase in net assets resulting from operations	(10,439,000)
Current assets	13,177,000
Non-current assets	40,311,000
Current liabilities	4,159,000
Non-current liabilities	15,711,000
Non-controlling interest	0
Stockholders’ equity	$ 33,618,000
Ownership percentage	90.00%
Clarion
Investment Company, Financial Highlights [Line Items]
Revenues	$ 676,000
Expenses	(1,857,000)
Income (loss) before taxes	(1,181,000)
Income tax expense	341,000
Consolidated net income (loss)	(840,000)
Net loss attributable to non-controlling interests	0
Net increase in net assets resulting from operations	(840,000)
Current assets	3,084,000
Non-current assets	66,182,000
Current liabilities	420,000
Non-current liabilities	22,500,000
Non-controlling interest	0
Stockholders’ equity	$ 46,346,000
Ownership percentage	99.00%
Other
Investment Company, Financial Highlights [Line Items]
Revenues	$ 118,256,000	$ 87,740,000
Expenses	(127,990,000)	(98,687,000)
Income (loss) before taxes	(9,734,000)	(10,947,000)
Income tax expense	875,000	3,117,000
Consolidated net income (loss)	(8,859,000)	(7,830,000)
Net loss attributable to non-controlling interests	0	0
Net increase in net assets resulting from operations	(8,859,000)	(7,830,000)
Current assets	64,792,000	51,902,000
Non-current assets	322,397,000	311,985,000
Current liabilities	41,781,000	35,927,000
Non-current liabilities	168,726,000	146,901,000
Non-controlling interest	0	0
Stockholders’ equity	$ 176,682,000	$ 181,059,000
Milton Industries, Inc.
Investment Company, Financial Highlights [Line Items]
Ownership percentage	13.00%	13.00%
Resolution Economics
Investment Company, Financial Highlights [Line Items]
Ownership percentage	8.00%	8.00%
Blue Ridge ESOP Associates
Investment Company, Financial Highlights [Line Items]
Ownership percentage	16.00%	17.00%