Document and Entity Information - shares	6 Months Ended
	Jul. 03, 2020	Aug. 05, 2020
Document and Entity Information
Document Type	10-Q
Document Quarterly Report	true
Document Transition Report	false
Document Period End Date	Jul. 03, 2020
Entity File Number	001-33076
Entity Registrant Name	WILLDAN GROUP, INC.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	14-1951112
Entity Address, Address Line One	2401 East Katella Avenue
Entity Address, Address Line Two	Suite 300
Entity Address, City or Town	Anaheim
Entity Address, Postal Zip Code	92806
Entity Address, State or Province	CA
City Area Code	800
Local Phone Number	424-9144
Title of 12(b) Security	Common Stock, par value $0.01 per share
Trading Symbol	WLDN
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 Common Stock, Shares Outstanding		12,065
Current Fiscal Year End Date	--01-01
Document Fiscal Period Focus	Q2
Document Fiscal Year Focus	2020
Entity Central Index Key	0001370450
Amendment Flag	false