Document and Entity Information - USD ($)	12 Months Ended
	Jan. 02, 2022	Mar. 04, 2022	Jul. 04, 2021
Document And Entity Information [Abstract]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Jan. 02, 2022
Document Transition Report	false
Entity File Number	001-35373
Entity Registrant Name	FIESTA RESTAURANT GROUP, INC.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	90-0712224
Entity Address, Address Line One	14800 Landmark Boulevard, Suite 500
Entity Address, City or Town	Dallas
Entity Address, State or Province	TX
Entity Address, Postal Zip Code	75254
City Area Code	972
Local Phone Number	702-9300
Title of 12(b) Security	Common Stock, par value $.01 per share
Trading Symbol	FRGI
Security Exchange Name	NASDAQ
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	true
Entity Shell Company	false
Entity Public Float			$ 250,298,984
Entity Common Stock, Shares Outstanding		25,707,125
Documents Incorporated by Reference	Portions of the registrant's definitive Proxy Statement for Fiesta Restaurant Group, Inc.'s 2022 Annual Meeting of Stockholders, which is expected to be filed pursuant to Regulation 14A no later than 120 days after the conclusion of Fiesta Restaurant Group, Inc.'s fiscal year ended January 2, 2022, are incorporated by reference into Part III of this annual report.
Entity Central Index Key	0001534992
Current Fiscal Year End Date	--01-02
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	FY
Amendment Flag	false