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Investment Portfolio (Details) (USD $) | Dec. 31, 2012 | Dec. 31, 2011
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Summary of market value of investments |  |
Total Investment Portfolio | $ 16,503,731 | $ 8,208,489
Diamond Hill Small Cap Fund [Member] |  |
Summary of market value of investments |  |
Total Investment Portfolio | 215,550 | 189,042
Diamond Hill Small-Mid Cap Fund [Member] |  |
Summary of market value of investments |  |
Total Investment Portfolio | 239,316 | 203,571
Diamond Hill Large Cap Fund [Member] |  |
Summary of market value of investments |  |
Total Investment Portfolio | 246,744 | 213,110
Diamond Hill Select Fund [Member] |  |
Summary of market value of investments |  |
Total Investment Portfolio | 242,252 | 214,833
Diamond Hill Long-Short Fund [Member] |  |
Summary of market value of investments |  |
Total Investment Portfolio | 1,036,045 | 212,720
Diamond Hill Research Opportunities Fund [Member] |  |
Summary of market value of investments |  |
Total Investment Portfolio | 10,658,665 |
Diamond Hill Strategic Income Fund [Member] |  |
Summary of market value of investments |  |
Total Investment Portfolio | 214,598 | 197,284
Diamond Hill Investment Partners, L.P. [Member] |  |
Summary of market value of investments |  |
Total Investment Portfolio | 7,336 | 156,122
Diamond Hill Investment Partners II, L.P. [Member] |  |
Summary of market value of investments |  |
Total Investment Portfolio |  | 131,203
Diamond Hill Research Partners, L.P. [Member] |  |
Summary of market value of investments |  |
Total Investment Portfolio |  | 5,770,874
Diamond Hill Research Partners - International, L.P. [Member] |  |
Summary of market value of investments |  |
Total Investment Portfolio | 1,384,976 | 919,730
Diamond Hill Valuation-Based Index L.P. [Member] |  |
Summary of market value of investments |  |
Total Investment Portfolio | $ 2,258,249 |

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- Definition Sum of the carrying amounts as of the balance sheet date of all investments. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03.1(h)) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 1 -Subparagraph h -Article 7 + Details
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