| **Document and Entity Information**            | 12 Months Ended          |
|------------------------------------------------|--------------------------|
||
| **Document and Entity Information [Abstract]** |                     |
| Document Type                                  | DEF 14A                  |
| Entity Registrant Name                         | NL INDUSTRIES, INC. |
| Entity Central Index Key                       | 0000072162               |
| Amendment Flag                                 | false                    |

| X                                                                                                                                                                                                                                                                                             |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Boolean flag that is true when the XBRL content amends previously-filed or accepted submission.
+ References
No definition available.
+ Details**Name:**dei_AmendmentFlag**Namespace Prefix:**dei_**Data Type:**xbrli:booleanItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                        |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Cover page.
+ References
No definition available.
+ Details**Name:**dei_CoverAbstract**Namespace Prefix:**dei_**Data Type:**xbrli:stringItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                    |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The type of document being provided (such as 10-K, 10-Q, 485BPOS, etc). The document type is limited to the same value as the supporting SEC submission type, or the word 'Other'.
+ References
No definition available.
+ Details**Name:**dei_DocumentType**Namespace Prefix:**dei_**Data Type:**dei:submissionTypeItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                            |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
A unique 10-digit SEC-issued value to identify entities that have filed disclosures with the SEC. It is commonly abbreviated as CIK.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Exchange Act -Number 240 -Section 12 -Subsection b-2
+ Details**Name:**dei_EntityCentralIndexKey**Namespace Prefix:**dei_**Data Type:**dei:centralIndexKeyItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                    |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The exact name of the entity filing the report as specified in its charter, which is required by forms filed with the SEC.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Exchange Act -Number 240 -Section 12 -Subsection b-2
+ Details**Name:**dei_EntityRegistrantName**Namespace Prefix:**dei_**Data Type:**xbrli:normalizedStringItemType**Balance Type:**na**Period Type:**duration |