| Document and Entity Information | Feb. 19, 2021 |
| Cover [Abstract] | |
| Amendment Flag | false |
| Entity Central Index Key | 0001678463 |
| Document Type | 8-K |
| Document Period End Date | Feb. 19, 2021 |
| Entity Registrant Name | FORTERRA, INC. |
| Entity Incorporation State Country Code | DE |
| Entity File Number | 001-37921 |
| Entity Tax Identification Number | 37-1830464 |
| Entity Address, Address Line One | 511 East John Carpenter Freeway |
| Entity Address, Address Line Two | 6th Floor |
| Entity Address, City or Town | Irving |
| Entity Address, State or Province | TX |
| Entity Address, Postal Zip Code | 75062 |
| City Area Code | (469) |
| Local Phone Number | 458-7973 |
| Written Communications | false |
| Soliciting Material | false |
| Pre Commencement Tender Offer | false |
| Pre Commencement Issuer Tender Offer | false |
| Security 12b Title | Common Stock, $0.001 Par Value |
| Trading Symbol | FRTA |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | false |
