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Investment Portfolio (Details) (USD $)	Mar. 31, 2013	Dec. 31, 2012
Summary of market value of investments
Total Investment Portfolio	$ 18,393,156	$ 16,503,731
Diamond Hill Small Cap Fund [Member]
Summary of market value of investments
Total Investment Portfolio	251,304	215,550
Diamond Hill Small-Mid Cap Fund [Member]
Summary of market value of investments
Total Investment Portfolio	279,021	239,316
Diamond Hill Large Cap Fund [Member]
Summary of market value of investments
Total Investment Portfolio	275,432	246,744
Diamond Hill Select Fund [Member]
Summary of market value of investments
Total Investment Portfolio	278,021	242,252
Diamond Hill Long-Short Fund [Member]
Summary of market value of investments
Total Investment Portfolio	1,125,816	1,036,045
Diamond Hill Research Opportunities Fund [Member]
Summary of market value of investments
Total Investment Portfolio	12,046,118	10,658,665
Diamond Hill Strategic Income Fund [Member]
Summary of market value of investments
Total Investment Portfolio	215,175	214,598
Diamond Hill Investment Partners, L.P. [Member]
Summary of market value of investments
Total Investment Portfolio	8,267	7,336
Diamond Hill Research Partners-International, L.P. [Member]
Summary of market value of investments
Total Investment Portfolio	1,438,872	1,384,976
Diamond Hill Valuation-Weighted 500, L.P. [Member]
Summary of market value of investments
Total Investment Portfolio	$ 2,475,130	$ 2,258,249