XML 11 R1.htm IDEA: XBRL DOCUMENT v3.23.2
Document And Entity Information - shares
 6 Months Ended
Jun. 30, 2023
Jul. 25, 2023
Document Information [Line Items]    
Entity Central Index Key 0001001385  
Entity Registrant Name Northwest Pipe Co.  
Amendment Flag false  
Current Fiscal Year End Date --12-31  
Document Fiscal Period Focus Q2  
Document Fiscal Year Focus 2023  
Document Type 10-Q  
Document Quarterly Report true  
Document Period End Date Jun. 30, 2023  
Document Transition Report false  
Entity File Number 0-27140  
Entity Incorporation, State or Country Code OR  
Entity Tax Identification Number 93-0557988  
Entity Address, Address Line One 201 NE Park Plaza Drive, Suite 100  
Entity Address, City or Town Vancouver  
Entity Address, State or Province WA  
Entity Address, Postal Zip Code 98684  
City Area Code 360  
Local Phone Number 397‑6250  
Title of 12(b) Security Common Stock, par value $0.01 per share  
Trading Symbol NWPX  
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   10,014,196