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Significant Accounting Policies - Revenues From Contracts with Customers (Details) - USD ($) | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2023 | Jun. 30, 2022 | Jun. 30, 2023 | Jun. 30, 2022
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue | $ 33,350,637 | $ 39,021,114 | $ 67,341,140 | $ 81,277,500
Investment advisory |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue | 31,500,443 | 36,408,165 | 63,542,902 | 75,687,051
Mutual fund administration, net |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue | 1,850,194 | 2,612,949 | 3,798,238 | 5,590,449
Diamond Hill Funds |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue | 22,771,617 | 28,060,071 | 46,103,204 | 58,292,499
Diamond Hill Funds | Investment advisory |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue | 20,921,423 | 25,447,122 | 42,304,966 | 52,702,050
Diamond Hill Funds | Mutual fund administration, net |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue | 1,850,194 | 2,612,949 | 3,798,238 | 5,590,449
Separately managed accounts |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue | 6,238,511 | 6,570,811 | 12,502,872 | 13,763,101
Separately managed accounts | Investment advisory |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue | 6,238,511 | 6,570,811 | 12,502,872 | 13,763,101
Separately managed accounts | Mutual fund administration, net |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue | 0 | 0 | 0 | 0
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 | 1,301,391 | 1,510,245 | 2,663,144 | 3,227,409
Model delivery | Investment advisory |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue | 1,301,391 | 1,510,245 | 2,663,144 | 3,227,409
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 | 836,095 | 508,271 | 1,737,216 | 1,053,766
Collective investment trusts | Investment advisory |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue | 836,095 | 508,271 | 1,737,216 | 1,053,766
Collective investment trusts | Mutual fund administration, net |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue | 0 | 0 | 0 | 0
Other Pooled Vehicles |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue | 2,203,023 | 2,371,716 | 4,334,704 | 4,940,725
Other Pooled Vehicles | Investment advisory |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue | $ 2,203,023 | $ 2,371,716 | $ 4,334,704 | $ 4,940,725

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