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Investment Portfolio - Summary of Market Value of Investments (Detail) - USD ($)	Sep. 30, 2015	Dec. 31, 2014
Investment Holdings [Line Items]
Total Investment Portfolio	$ 52,694,353	$ 45,427,456
Seed Capital Investments
Investment Holdings [Line Items]
Total Investment Portfolio	43,179,666	39,748,692
Seed Capital Investments | Diamond Hill Research Opportunities Fund
Investment Holdings [Line Items]
Total Investment Portfolio	11,196,494	13,143,281
Seed Capital Investments | Diamond Hill Mid Cap Fund
Investment Holdings [Line Items]
Total Investment Portfolio	10,619,840	10,729,930
Seed Capital Investments | Diamond Hill Financial Long-Short Fund
Investment Holdings [Line Items]
Total Investment Portfolio	951,064	1,222,892
Seed Capital Investments | Diamond Hill Valuation- Weighted 500 ETF
Investment Holdings [Line Items]
Total Investment Portfolio	9,033,120	0
Seed Capital Investments | Diamond Hill Valuation-Weighted 500, L.P.
Investment Holdings [Line Items]
Total Investment Portfolio	0	3,398,035
Seed Capital Investments | Diamond Hill High Yield Fund, L.P.
Investment Holdings [Line Items]
Total Investment Portfolio	9,964,462	9,764,814
Seed Capital Investments | Diamond Hill Global Fund, L.P.
Investment Holdings [Line Items]
Total Investment Portfolio	1,414,686	1,489,740
Investments in Deferred Compensation Plans
Investment Holdings [Line Items]
Total Investment Portfolio	$ 9,514,687	$ 5,678,764

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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

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