Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2015	Oct. 20, 2015
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2015
Document Fiscal Year Focus	2015
Document Fiscal Period Focus	Q3
Trading Symbol	TREX
Entity Registrant Name	TREX CO INC
Entity Central Index Key	0001069878
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		30,866,899