| Document and Entity Information | Dec. 30, 2022 |
| Cover [Abstract] | |
| Entity Registrant Name | TREX CO INC |
| Amendment Flag | false |
| Entity Central Index Key | 0001069878 |
| Document Type | 8-K |
| Document Period End Date | Dec. 30, 2022 |
| Entity Incorporation State Country Code | DE |
| Entity File Number | 001-14649 |
| Entity Tax Identification Number | 54-1910453 |
| Entity Address, Address Line One | 160 Exeter Drive |
| Entity Address, City or Town | Winchester |
| Entity Address, State or Province | VA |
| Entity Address, Postal Zip Code | 22603-8605 |
| City Area Code | (540) |
| Local Phone Number | 542-6300 |
| Security 12b Title | Common stock |
| Trading Symbol | TREX |
| Security Exchange Name | NYSE |
| Written Communications | false |
| Soliciting Material | false |
| Pre Commencement Tender Offer | false |
| Pre Commencement Issuer Tender Offer | false |
| Entity Emerging Growth Company | false |
