Share-Based Compensation Arrangement By Share-Based Payment Award, Award Measurement Period

No definition available.

Name:	nwli_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardMeasurementPeriod
Namespace Prefix:	nwli_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Share-Based Compensation Arrangement By Share-Based Payment Award, Options, Extensions In Period

+ References

No definition available.

+ Details

Name:	nwli_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExtensionsInPeriod
Namespace Prefix:	nwli_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Share-Based Compensation Arrangement By Share-Based Payment Award, Performance Factor, Percentage Of Pre-Defined Metric Target

+ References

No definition available.

+ Details

Name:	nwli_ShareBasedCompensationArrangementByShareBasedPaymentAwardPerformanceFactorPercentageOfPreDefinedMetricTarget
Namespace Prefix:	nwli_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Share-Based Compensation Arrangement By Share-Based Payment Award, Vesting Price Determining Period

+ References

No definition available.

+ Details

Name:	nwli_ShareBasedCompensationArrangementByShareBasedPaymentAwardVestingPriceDeterminingPeriod
Namespace Prefix:	nwli_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Share-Based Payment, Performance Outcome Period

+ References

No definition available.

+ Details

Name:	nwli_ShareBasedPaymentPerformanceOutcomePeriod
Namespace Prefix:	nwli_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Share-Based Payment, Performance Period

+ References

No definition available.

+ Details

Name:	nwli_ShareBasedPaymentPerformancePeriod
Namespace Prefix:	nwli_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (h)(1)(i)
-URI https://asc.fasb.org/extlink&oid=128089324&loc=d3e5070-113901

+ Details

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

- Definition

Face amount or stated value per share of common stock.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(29))
-URI https://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

Name:	us-gaap_CommonStockParOrStatedValuePerShare
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:perShareItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount of cost not yet recognized for nonvested award under share-based payment arrangement.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (i)
-URI https://asc.fasb.org/extlink&oid=128089324&loc=d3e5070-113901

+ Details

Name:	us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Weighted-average period over which cost not yet recognized is expected to be recognized for award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (i)
-URI https://asc.fasb.org/extlink&oid=128089324&loc=d3e5070-113901

+ Details

Name:	us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of cost to be recognized for option under share-based payment arrangement.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (i)
-URI https://asc.fasb.org/extlink&oid=128089324&loc=d3e5070-113901

+ Details

Name:	us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of tax benefit for recognition of expense of award under share-based payment arrangement.

+ References

+ Details

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

- Definition

Amount of cash inflow from exercise of option under share-based payment arrangement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2A
-Subparagraph (a)
-URI https://asc.fasb.org/extlink&oid=128089324&loc=SL79508275-113901

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 14
-Subparagraph (a)
-URI https://asc.fasb.org/extlink&oid=126954810&loc=d3e3255-108585

+ Details

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

- Definition

Estimated period over which an employee is required to provide service in exchange for the equity-based payment award, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)(1)
-URI https://asc.fasb.org/extlink&oid=128089324&loc=d3e5070-113901

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardRequisiteServicePeriod1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Period over which grantee's right to exercise award under share-based payment arrangement is no longer contingent on satisfaction of service or performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, combination of market, performance or service condition.

+ References

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of shares authorized for issuance under share-based payment arrangement.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)(3)
-URI https://asc.fasb.org/extlink&oid=128089324&loc=d3e5070-113901

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (d)(2)
-URI https://asc.fasb.org/extlink&oid=128089324&loc=d3e5070-113901

+ Details

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

- Definition

Price of a single share of a number of saleable stocks of a company.

+ References

No definition available.

+ Details

Name:	us-gaap_SharePrice
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:perShareItemType
Balance Type:	na
Period Type:	instant

- Definition

Percentage of vesting of award under share-based payment arrangement.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)(1)
-URI https://asc.fasb.org/extlink&oid=128089324&loc=d3e5070-113901

+ Details

Name:	us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Fair value of options vested. Excludes equity instruments other than options, for example, but not limited to, share units, stock appreciation rights, restricted stock.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (d)(2)
-URI https://asc.fasb.org/extlink&oid=128089324&loc=d3e5070-113901

+ Details

Name:	us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedInPeriodFairValue1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

Name:	us-gaap_AwardTypeAxis=nwli_EmployeeStockAppreciationRightsSARsGrantedBefore2016Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_TitleOfIndividualAxis=nwli_EmployeesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardTypeAxis=nwli_EmployeeStockAppreciationRightsSARsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardTypeAxis=nwli_EmployeeStockOptionsandStockAppreciationRightsSARsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_TitleOfIndividualAxis=srt_DirectorMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardTypeAxis=us-gaap_RestrictedStockUnitsRSUMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardTypeAxis=us-gaap_PerformanceSharesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VestingAxis=us-gaap_ShareBasedCompensationAwardTrancheOneMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VestingAxis=us-gaap_ShareBasedCompensationAwardTrancheTwoMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VestingAxis=us-gaap_ShareBasedCompensationAwardTrancheThreeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VestingAxis=nwli_ShareBasedPaymentArrangementTrancheFourMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VestingAxis=nwli_ShareBasedPaymentArrangementTrancheFiveMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementClassOfStockAxis=us-gaap_CommonClassAMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PlanNameAxis=nwli_IncentivePlanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Share-Based Payments - Narrative (Details) - USD ($)	3 Months Ended		6 Months Ended		12 Months Ended
Share-Based Payments - Narrative (Details) - USD ($)	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Term of extension							10 years
Compensation cost not yet recognized	$ 9,300,000		$ 9,300,000		$ 7,900,000
Total intrinsic value of options exercised			1,100,000	$ 2,000,000
Fair value of vested awards			100,000	0
Cash received from exercise of stock options			$ 0	0
Closing stock price (in dollars per share)	$ 202.70		$ 202.70
Pre-tax compensation cost (benefit) recognized	$ 1,000,000	$ (500,000)	$ 2,500,000	3,900,000
Compensation cost (benefit), tax expense (benefit)	(200,000)	$ 100,000	(500,000)	$ (800,000)
Compensation cost related to nonvested options not yet recognized	$ 8,500,000		$ 8,500,000
Weighted average period over which the compensation is expected to be recognized			1 year 2 months 12 days
Employee SARs granted before 2016 \| Employees
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Requisite service period of awards			3 years
Employee SARs \| Employees
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Requisite service period of awards			1 year
Employee Stock Options and SARs \| Directors
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Requisite service period of awards			1 year
RSU \| Employees
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage			100.00%
Vesting period			3 years
RSU \| Directors
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period			1 year
PSU
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period			3 years
Performance period			3 years
Performance outcome period			3 years
Award measurement period					3 years	3 years
Performance factor used to determine compensation payout percentage					110.19%	85.16%
Vesting Service Period, Trench One \| Employee SARs granted before 2016 \| Employees
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage			20.00%
Vesting Service Period, Trench One \| Employee SARs \| Employees
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage			33.30%
Vesting Service Period, Trench One \| Employee Stock Options and SARs \| Directors
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage			20.00%
Vesting Service Period, Trench One \| RSU \| Employees
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Requisite service period of awards			3 years
Vesting Service Period, Trench Two \| Employee SARs granted before 2016 \| Employees
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage			20.00%
Vesting Service Period, Trench Two \| Employee SARs \| Employees
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage			33.30%
Vesting Service Period, Trench Two \| Employee Stock Options and SARs \| Directors
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage			20.00%
Vesting Service Period, Trench Two \| RSU \| Employees
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Requisite service period of awards			3 years
Vesting Service Period, Trench Three \| Employee SARs granted before 2016 \| Employees
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage			20.00%
Vesting Service Period, Trench Three \| Employee SARs \| Employees
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage			33.30%
Vesting Service Period, Trench Three \| Employee Stock Options and SARs \| Directors
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage			20.00%
Vesting Service Period, Trench Four \| Employee SARs granted before 2016 \| Employees
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage			20.00%
Vesting Service Period, Trench Four \| Employee Stock Options and SARs \| Directors
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage			20.00%
Vesting Service Period, Trench Five \| Employee SARs granted before 2016 \| Employees
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage			20.00%
Vesting Service Period, Trench Five \| Employee Stock Options and SARs \| Directors
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage			20.00%
Class A
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock, par value (in dollars per share)	$ 0.01		$ 0.01		$ 0.01
Award vesting price determining period			20 days
Class A \| RSU \| Directors
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting price determining period			20 days
Class A \| PSU
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting price determining period			20 days
Class A \| Vesting Service Period, Trench Two \| RSU \| Employees
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting price determining period			20 days
Class A \| Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock, par value (in dollars per share)							$ 1.00
Share-based payments, number of shares authorized under plans (in shares)							300,000