Significant Accounting Policies - Revenues From Contracts with Customers (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Disaggregation of Revenue [Line Items]
Revenue	$ 39,018,232	$ 35,554,280	$ 111,974,495	$ 102,895,420
Investment advisory
Disaggregation of Revenue [Line Items]
Revenue	37,229,875	33,668,351	106,422,793	97,211,253
Mutual fund administration, net
Disaggregation of Revenue [Line Items]
Revenue	1,788,357	1,885,929	5,551,702	5,684,167
Diamond Hill Funds
Disaggregation of Revenue [Line Items]
Revenue	25,383,561	23,600,801	73,801,464	69,704,006
Diamond Hill Funds \| Investment advisory
Disaggregation of Revenue [Line Items]
Revenue	23,595,204	21,714,872	68,249,762	64,019,839
Diamond Hill Funds \| Mutual fund administration, net
Disaggregation of Revenue [Line Items]
Revenue	1,788,357	1,885,929	5,551,702	5,684,167
Separately managed accounts, excluding performance-based fees
Disaggregation of Revenue [Line Items]
Revenue	6,698,073	6,150,388	20,083,201	18,653,260
Separately managed accounts, excluding performance-based fees \| Investment advisory
Disaggregation of Revenue [Line Items]
Revenue	6,698,073	6,150,388	20,083,201	18,653,260
Separately managed accounts, excluding 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	2,878,015	2,451,019	8,522,431	6,785,722
Other pooled vehicles \| Investment advisory
Disaggregation of Revenue [Line Items]
Revenue	2,878,015	2,451,019	8,522,431	6,785,722
Other pooled vehicles \| Mutual fund administration, net
Disaggregation of Revenue [Line Items]
Revenue	0	0	0	0
Collective investment trusts
Disaggregation of Revenue [Line Items]
Revenue	1,839,850	1,306,460	4,805,245	2,606,477
Collective investment trusts \| Investment advisory
Disaggregation of Revenue [Line Items]
Revenue	1,839,850	869,261	4,805,245	2,606,477
Collective investment trusts \| Mutual fund administration, net
Disaggregation of Revenue [Line Items]
Revenue	0	0	0	0
Model delivery
Disaggregation of Revenue [Line Items]
Revenue	1,331,016	869,261	3,874,437	3,969,604
Model delivery \| Investment advisory
Disaggregation of Revenue [Line Items]
Revenue	1,331,016	1,306,460	3,874,437	3,969,604
Model delivery \| Mutual fund administration, net
Disaggregation of Revenue [Line Items]
Revenue	0	0	0	0
Performance-Based Fees
Disaggregation of Revenue [Line Items]
Revenue	887,717	1,176,351	887,717	1,176,351
Performance-Based Fees \| Investment advisory
Disaggregation of Revenue [Line Items]
Revenue	887,717	1,176,351	887,717	1,176,351
Performance-Based Fees \| Mutual fund administration, net
Disaggregation of Revenue [Line Items]
Revenue	$ 0	$ 0	$ 0	$ 0