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Investment Portfolio - Summary of Market Value of Investments (Detail) (USD $)	Sep. 30, 2014	Dec. 31, 2013
Investment Holdings [Line Items]
Total Investment Portfolio	$ 34,989,899	$ 18,726,070
Seed Capital Investments
Investment Holdings [Line Items]
Total Investment Portfolio	29,685,276	17,438,325
Seed Capital Investments | Diamond Hill Research Opportunities Fund
Investment Holdings [Line Items]
Total Investment Portfolio	13,619,318	13,305,830
Seed Capital Investments | Diamond Hill Mid Cap Fund
Investment Holdings [Line Items]
Total Investment Portfolio	10,199,901	0
Seed Capital Investments | Diamond Hill Valuation-Weighted 500, L.P.
Investment Holdings [Line Items]
Total Investment Portfolio	3,259,028	3,000,328
Seed Capital Investments | Diamond Hill Global Fund, L.P.
Investment Holdings [Line Items]
Total Investment Portfolio	1,452,249	0
Seed Capital Investments | Diamond Hill Financial Long-Short Fund
Investment Holdings [Line Items]
Total Investment Portfolio	1,154,780	1,131,034
Seed Capital Investments | Diamond Hill Investment Partners, L.P.
Investment Holdings [Line Items]
Total Investment Portfolio	0	1,133
Investments in Deferred Compensation Plans
Investment Holdings [Line Items]
Total Investment Portfolio	$ 5,304,623	$ 1,287,745

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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

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