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Significant Accounting Policies - Revenue From Contracts with Customers (Details) - USD ($) | 12 Months Ended
--- | ---
Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2021
Disaggregation of Revenue [Line Items] |  |  |
Revenue | $ 136,716,371 | $ 154,496,019 | $ 182,193,837
Investment advisory |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenue | 129,179,500 | 144,325,517 | 170,137,609
Mutual fund administration, net |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenue | 7,536,871 | 10,170,502 | 12,056,228
Diamond Hill Funds |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenue | 92,347,323 | 109,044,073 | 125,658,545
Diamond Hill Funds | Investment advisory |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenue | 84,810,452 | 98,873,571 | 113,602,317
Diamond Hill Funds | Mutual fund administration, net |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenue | 7,536,871 | 10,170,502 | 12,056,228
Separately managed accounts, excluding performance-based fees |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenue | 24,898,695 | 26,200,724 | 27,882,488
Separately managed accounts, excluding performance-based fees | Investment advisory |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenue | 24,898,695 | 26,200,724 | 27,882,488
Separately managed accounts, excluding performance-based fees | Mutual fund administration, net |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenue | 0 | 0 | 0
Performance-based fees |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenue | 1,176,351 | 1,500,225 | 11,860,051
Performance-based fees | Investment advisory |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenue | 1,176,351 | 1,500,225 | 11,860,051
Performance-based fees | Mutual fund administration, net |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenue | 0 | 0 | 0
Other pooled vehicles |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenue | 9,261,533 | 9,410,541 | 10,166,928
Other pooled vehicles | Investment advisory |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenue | 9,261,533 | 9,410,541 | 10,166,928
Other pooled vehicles | Mutual fund administration, net |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenue | 0 | 0 | 0
Model delivery |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenue | 5,211,113 | 5,910,061 | 4,977,234
Model delivery | Investment advisory |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenue | 5,211,113 | 5,910,061 | 4,977,234
Model delivery | Mutual fund administration, net |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenue | 0 | 0 | 0
Collective investment trusts |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenue | 3,821,356 | 2,430,395 | 1,648,591
Collective investment trusts | Investment advisory |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenue | 3,821,356 | 2,430,395 | 1,648,591
Collective investment trusts | Mutual fund administration, net |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenue | $ 0 | $ 0 | $ 0

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