Document and Entity Information	6 Months Ended
	Jun. 30, 2014	Aug. 01, 2014
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Jun. 30, 2014
Document Fiscal Year Focus	2014
Document Fiscal Period Focus	Q2
Trading Symbol	NWPX
Entity Registrant Name	NORTHWEST PIPE CO
Entity Central Index Key	0001001385
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Entity Common Stock, Shares Outstanding		9,518,557