Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Feb. 22, 2023	Jun. 30, 2022
Cover [Abstract]
Document Type	10-K
Amendment Flag	false
Document Annual Report	true
Document Transition Report	false
Document Fiscal Year Focus	2022
Document Fiscal Period Focus	FY
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	Yes
Document Period End Date	Dec. 31, 2022
Entity Registrant Name	First Financial Bankshares, Inc.
Entity Central Index Key	0000036029
Entity Filer Category	Large Accelerated Filer
Entity Interactive Data Current	Yes
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity File Number	0-07674
Entity Incorporation, State or Country Code	TX
Entity Tax Identification Number	75-0944023
Entity Address, Address Line One	400 Pine Street
Entity Address, City or Town	Abilene
Entity Address, State or Province	TX
City Area Code	325
Local Phone Number	627-7155
Entity Shell Company	false
Entity Small Business	false
Entity Emerging Growth Company	false
Title of 12(b) Security	Common Stock, par value $0.01 per share
Trading Symbol	FFIN
Security Exchange Name	NASDAQ
Entity Address, Postal Zip Code	79601
Entity Common Stock, Shares Outstanding		142,701,017
Entity Public Float			$ 5,370
ICFR Auditor Attestation Flag	true
Documents Incorporated by Reference	Certain information required by Part III is incorporated by reference to the proxy statement for our 2023 annual meeting of shareholders, which will be filed with the Securities and Exchange Commission not later than 120 days after December 31, 2022.
Auditor Location	Fort Worth, Texas
Auditor Name	Ernst & Young LLP
Auditor Firm ID	42