Significant Accounting Policies - Revenues From Contracts with Customers (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Disaggregation of Revenue [Line Items]
Revenue	$ 35,554,280	$ 38,264,674	$ 102,895,420	$ 119,542,174
Investment advisory
Disaggregation of Revenue [Line Items]
Revenue	33,668,351	35,842,083	97,211,253	111,529,134
Mutual fund administration, net
Disaggregation of Revenue [Line Items]
Revenue	1,885,929	2,422,591	5,684,167	8,013,040
Diamond Hill Funds
Disaggregation of Revenue [Line Items]
Revenue	23,600,801	26,495,289	69,704,006	84,787,789
Diamond Hill Funds \| Investment advisory
Disaggregation of Revenue [Line Items]
Revenue	21,714,872	24,072,698	64,019,839	76,774,749
Diamond Hill Funds \| Mutual fund administration, net
Disaggregation of Revenue [Line Items]
Revenue	1,885,929	2,422,591	5,684,167	8,013,040
Separately managed accounts, excluding performance-based fees
Disaggregation of Revenue [Line Items]
Revenue	6,150,388	6,163,236	18,653,260	19,926,337
Separately managed accounts, excluding performance-based fees \| Investment advisory
Disaggregation of Revenue [Line Items]
Revenue	6,150,388	6,163,236	18,653,260	19,926,337
Separately managed accounts, excluding performance-based fees \| Mutual fund administration, net
Disaggregation of Revenue [Line Items]
Revenue	0	0	0	0
Performance-based fees
Disaggregation of Revenue [Line Items]
Revenue	1,176,351	1,500,225	1,176,351	1,500,225
Performance-based fees \| Investment advisory
Disaggregation of Revenue [Line Items]
Revenue	1,176,351	1,500,225	1,176,351	1,500,225
Performance-based fees \| Mutual fund administration, net
Disaggregation of Revenue [Line Items]
Revenue	0	0	0	0
Other pooled vehicles
Disaggregation of Revenue [Line Items]
Revenue	2,451,019	2,260,465	6,785,722	7,201,190
Other pooled vehicles \| Investment advisory
Disaggregation of Revenue [Line Items]
Revenue	2,451,019	2,260,465	6,785,722	7,201,190
Other pooled vehicles \| Mutual fund administration, net
Disaggregation of Revenue [Line Items]
Revenue	0	0	0	0
Model delivery
Disaggregation of Revenue [Line Items]
Revenue	1,306,460	1,358,517	3,969,604	4,585,925
Model delivery \| Investment advisory
Disaggregation of Revenue [Line Items]
Revenue	1,306,460	1,358,517	3,969,604	4,585,925
Model delivery \| Mutual fund administration, net
Disaggregation of Revenue [Line Items]
Revenue	0	0	0	0
Collective investment trusts
Disaggregation of Revenue [Line Items]
Revenue	869,261	486,942	2,606,477	1,540,708
Collective investment trusts \| Investment advisory
Disaggregation of Revenue [Line Items]
Revenue	869,261	486,942	2,606,477	1,540,708
Collective investment trusts \| Mutual fund administration, net
Disaggregation of Revenue [Line Items]
Revenue	$ 0	$ 0	$ 0	$ 0