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Cover
Dec. 10, 2025
Cover [Abstract]  
Document Type 8-K
Amendment Flag false
Document Period End Date Dec. 10, 2025
Entity File Number 000-24498
Entity Registrant Name Diamond Hill Investment Group, Inc.
Entity Central Index Key 0000909108
Entity Tax Identification Number 65-0190407
Entity Incorporation, State or Country Code OH
Entity Address, Address Line One 325 John H. McConnell Blvd
Entity Address, Address Line Two Suite 200
Entity Address, City or Town Columbus
Entity Address, State or Province OH
Entity Address, Postal Zip Code 43215
City Area Code 614
Local Phone Number 255-3333
Written Communications false
Soliciting Material true
Pre-commencement Tender Offer false
Pre-commencement Issuer Tender Offer false
Title of 12(b) Security Common Stock, no par value
Trading Symbol DHIL
Security Exchange Name NASDAQ
Entity Emerging Growth Company false