Document and Entity Information - shares	3 Months Ended
	Apr. 03, 2022	May 06, 2022
Document And Entity Information [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Apr. 03, 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 $0.01 per share
Entity Trading Symbol	FRGI
Security Exchange Name	NASDAQ
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Central Index Key	0001534992
Current Fiscal Year End Date	--01-01
Document Fiscal Year Focus	2022
Document Fiscal Period Focus	Q1
Amendment Flag	false
Entity Common Stock, Shares Outstanding		25,918,554