| Document and Entity Information | Apr. 20, 2020 |
| Cover page. | |
| Amendment Flag | false |
| Entity Central Index Key | 0001486957 |
| Document Type | 8-K |
| Document Period End Date | Apr. 20, 2020 |
| Entity Registrant Name | BWX TECHNOLOGIES, INC. |
| Entity Incorporation, State or Country Code | DE |
| Entity File Number | 001-34658 |
| Entity Tax Identification Number | 80-0558025 |
| Entity Address, Address Line One | 800 Main Street, 4th Floor |
| Entity Address, City or Town | Lynchburg, |
| Entity Address, State or Province | VA |
| Entity Address, Postal Zip Code | 24504 |
| City Area Code | 980 |
| Local Phone Number | 365-4300 |
| Written Communications | false |
| Soliciting Material | true |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common Stock, $0.01 par value |
| Trading Symbol | BWXT |
| Security Exchange Name | NYSE |
| Entity Emerging Growth Company | false |
