v3.10.0.1
Document and Entity Information - shares
6 Months Ended
Jun. 29, 2018
Aug. 02, 2018
Document and Entity Information    
Entity Registrant Name Willdan Group, Inc.  
Entity Central Index Key 0001370450  
Document Type 10-Q  
Document Period End Date Jun. 29, 2018  
Amendment Flag false  
Current Fiscal Year End Date --12-28  
Entity Current Reporting Status Yes  
Entity Filer Category Accelerated Filer  
Entity Common Stock, Shares Outstanding   8,913,114
Document Fiscal Year Focus 2018  
Document Fiscal Period Focus Q2