Investment Portfolio - Summary of Cash and Cash Equivalent Investments, Excluding Money Market Funds (Details) (USD $)	Dec. 31, 2013		Dec. 31, 2012
Summary of market value of investments
Total Investment Portfolio	$ 18,726,070		$ 16,503,731
Diamond Hill Small Cap Fund
Summary of market value of investments
Total Investment Portfolio	0		215,550
Diamond Hill Small-Mid Cap Fund
Summary of market value of investments
Total Investment Portfolio	0		239,316
Diamond Hill Large Cap Fund
Summary of market value of investments
Total Investment Portfolio	0		246,744
Diamond Hill Select Fund
Summary of market value of investments
Total Investment Portfolio	0		242,252
Diamond Hill Long-Short Fund
Summary of market value of investments
Total Investment Portfolio	1,287,745		1,036,045
Diamond Hill Financial Long-Short Fund
Summary of market value of investments
Total Investment Portfolio	1,131,034		0
Diamond Hill Research Opportunities Fund
Summary of market value of investments
Total Investment Portfolio	13,305,830		10,658,665
Diamond Hill Strategic Income Fund
Summary of market value of investments
Total Investment Portfolio	0		214,598
Diamond Hill Investment Partners, L.P.
Summary of market value of investments
Total Investment Portfolio	1,133		7,336
Diamond Hill Global Fund, L.P.(a)
Summary of market value of investments
Total Investment Portfolio	0	[1]	1,384,976	[1]
Diamond Hill Valuation-Weighted 500, L.P.
Summary of market value of investments
Total Investment Portfolio	$ 3,000,328		$ 2,258,249

[1] Diamond Hill Global Fund, L.P. ("DHGF"), formerly Diamond Hill Research Partners – International, L.P.