Component of other income and expense.

No definition available.

Name:	nl_ComponentOfOtherIncomeAndExpenseLineItems
Namespace Prefix:	nl_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of insurance carriers.

+ References

No definition available.

+ Details

Name:	nl_NumberOfInsuranceCarriers
Namespace Prefix:	nl_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of gain (loss) from sale and disposal of integrated set of activities and assets capable of being conducted and managed for purpose of providing return in form of dividend, lower cost, or other economic benefit to investor, owner, member and participant.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3602-108585

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 50
-Paragraph 1B
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109239629&loc=SL4582445-111684

+ Details

Name:	us-gaap_GainLossOnSaleOfBusiness
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The net amount of other operating income and expenses, the components of which are not separately disclosed on the income statement, from items that are associated with the entity's normal revenue producing operations.

+ References

No definition available.

+ Details

Name:	us-gaap_OtherOperatingIncomeExpenseNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The cash inflow associated with the amount received from the sale of a portion of the company's business, for example a segment, division, branch or other business, during the period.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 12
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3179-108585

+ Details

Name:	us-gaap_ProceedsFromDivestitureOfBusinesses
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

Name:	us-gaap_NoncashOrPartNoncashDivestituresByUniqueNameAxis=nl_InsuranceAndRiskManagementBusinessMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis=nl_SaleOfExcessPropertyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Other Operating Income (Expense) - Additional Information (Detail) $ in Thousands	3 Months Ended		12 Months Ended
	Dec. 31, 2019 USD ($)	Sep. 30, 2019 USD ($)	Dec. 31, 2020 USD ($) InsuranceCarrier	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Component Of Other Income And Expense [Line Items]
Number of insurance carriers for which agreed to reimburse litigation costs \| InsuranceCarrier			1
Other income, net			$ 18	$ 7,444	$ 644
Proceeds from sale of business				2,925
Gain from sale of business				$ 3,000
Insurance and Risk Management Business
Component Of Other Income And Expense [Line Items]
Proceeds from sale of business	$ 3,250
Gain from sale of business	$ 3,000
Sale of Excess Property
Component Of Other Income And Expense [Line Items]
Other income, net		$ 4,400