Document and Entity Information - shares
6 Months Ended
Jun. 30, 2018
Jul. 27, 2018
Document And Entity Information [Abstract]    
Entity Registrant Name NANOMETRICS INC  
Entity Central Index Key 0000704532  
Document Type 10-Q  
Document Period End Date Jun. 30, 2018  
Amendment Flag false  
Document Fiscal Year Focus 2018  
Document Fiscal Period Focus Q2  
Trading Symbol NANO  
Current Fiscal Year End Date --12-29  
Entity Filer Category Accelerated Filer  
Entity Common Stock, Shares Outstanding   24,136,582