Business and Organization	6 Months Ended
Jun. 30, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Business and Organization	Business and OrganizationDiamond Hill Investment Group, Inc. (the "Company"), an Ohio corporation, derives consolidated revenue and net income from investment advisory and fund administration services. Diamond Hill Capital Management, Inc. ("DHCM"), an Ohio corporation, is a wholly owned subsidiary of the Company and a registered investment adviser. DHCM is the investment adviser to the Diamond Hill Funds (the "Funds"), a series of open-end mutual funds. DHCM is also administrator for the Funds. The Company also provides investment advisory services to separately managed accounts and provides sub-advisory services to other mutual funds.

The entire disclosure for organization, consolidation and basis of presentation of financial statements disclosure.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 205
-URI http://asc.fasb.org/topic&trid=2122149

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-URI http://asc.fasb.org/topic&trid=2197479

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