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This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 97 -Paragraph 15-21 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 6: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 113 -Paragraph 26 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. false2Future policy benefits31false 5us-gaap_PolicyholderFundsus-gaap_truecreditinstantfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truefalsefalse1310900013109USD$falsefalsefalse2truefalsefalse1189900011899USD$falsefalsefalse3truefalsefalse1310900013109USD$falsefalsefalse4truefalsefalse1189900011899USD$falsefalsefalse5falsefalsefalse00falsefalsefalsexbrli:monetaryItemTypemonetaryThe total liability as of the balance sheet date of amounts due policy holders, excluding future policy benefits and claims, including unpaid policy dividends, retrospective refunds, and undistributed earnings on participating business.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03.13,14) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 false2Other policyholder liabilities32true 4us-gaap_IncomeStatementAbstractus-gaap_truenadurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1falsefalsefalse00falsefalsefalse2falsefalsefalse00falsefalsefalse3falsefalsefalse00falsefalsefalse4falsefalsefalse00falsefalsefalse5falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringfalse0Condensed Consolidated Income Statements:33false 5nwli_PremiumsEarnedAndPolicyChargesnwli_falsecreditdurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truefalsefalse94130009413USD$falsefalsefalse2truefalsefalse42800004280USD$falsefalsefalse3truefalsefalse1902300019023USD$falsefalsefalse4truefalsefalse1481900014819USD$falsefalsefalse5falsefalsefalse00falsefalsefalsexbrli:monetaryItemTypemonetaryPremiums earned and policy chargesNo definition available.false2Premiums and contract revenues34false 5us-gaap_NetInvestmentIncomeus-gaap_truecreditdurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truefalsefalse82420008242USD$falsefalsefalse2truefalsefalse39910003991USD$falsefalsefalse3truefalsefalse1601500016015USD$falsefalsefalse4truefalsefalse98090009809USD$falsefalsefalse5falsefalsefalse00falsefalsefalsexbrli:monetaryItemTypemonetaryThe income earned from investments in securities and property, equipment and other capital assets. 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This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. false2Amortization of deferred acquisition costs39false 5us-gaap_InterestCreditedToPolicyholdersAccountBalancesus-gaap_truedebitdurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truefalsefalse78680007868USD$falsefalsefalse2truefalsefalse12300001230USD$falsefalsefalse3truefalsefalse1505900015059USD$falsefalsefalse4truefalsefalse84430008443USD$falsefalsefalse5falsefalsefalse00falsefalsefalsexbrli:monetaryItemTypemonetaryInterest allocated to policyholders holding contracts under which the insurer must provide a guaranteed yield.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 225 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-04.6) -URI http://asc.fasb.org/extlink&oid=6879464&loc=d3e573970-122913 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 20 -Section 45 -Paragraph 2 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=6480726&loc=d3e6691-158385 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 97 -Paragraph 21 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. 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Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Paragraph 6 -Article 7 false2Universal life and annuity contract interest40false 5us-gaap_OtherCostAndExpenseOperatingus-gaap_truedebitdurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truefalsefalse49470004947USD$falsefalsefalse2truefalsefalse25780002578USD$falsefalsefalse3truefalsefalse87140008714USD$falsefalsefalse4truefalsefalse73460007346USD$falsefalsefalse5falsefalsefalse00falsefalsefalsexbrli:monetaryItemTypemonetaryThe total amount of other operating cost and expense items that are associated with the entity's normal revenue producing operation.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 225 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03.3) -URI http://asc.fasb.org/extlink&oid=6880815&loc=d3e20235-122688 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 3 -Article 5 false2Other operating expenses41false 5nwli_SegmentReportingInformationIncomeTaxesExpenseBenefitnwli_falsedebitdurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truefalsefalse468000468USD$falsefalsefalse2truefalsefalse261000261USD$falsefalsefalse3truefalsefalse938000938USD$falsefalsefalse4truefalsefalse376000376USD$falsefalsefalse5falsefalsefalse00falsefalsefalsexbrli:monetaryItemTypemonetarySegment Reporting Information, Income Taxes Expense (Benefit)No definition available.false2Federal income taxes (benefit)42false 5us-gaap_OperatingExpensesus-gaap_truedebitdurationfalsefalsefalsefalsefalsefalsefalsefalsetotalLabel1truefalsefalse1658900016589USD$falsefalsefalse2truefalsefalse77570007757USD$falsefalsefalse3truefalsefalse3308200033082USD$falsefalsefalse4truefalsefalse2389200023892USD$falsefalsefalse5falsefalsefalse00falsefalsefalsexbrli:monetaryItemTypemonetaryGenerally recurring costs associated with normal operations except for the portion of these expenses which can be clearly related to production and included in cost of sales or services. 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This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. false2Total segment assets48false 5us-gaap_LiabilityForFuturePolicyBenefitsus-gaap_truecreditinstantfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truefalsefalse875672000875672USD$falsefalsefalse2truefalsefalse795992000795992USD$falsefalsefalse3truefalsefalse875672000875672USD$falsefalsefalse4truefalsefalse795992000795992USD$falsefalsefalse5falsefalsefalse00falsefalsefalsexbrli:monetaryItemTypemonetaryThe sum of the known and estimated amounts payable as of the balance sheet date to policyholders pertaining to insured events for long-duration contracts, which can be viewed as either (a) the present value of future benefits to be paid to or on behalf of policyholders and expenses less the present value of future net premiums payable under the insurance contracts or (b) the accumulated amount of net premiums already collected less the accumulated amount of benefits and expenses already paid to or on behalf of policyholders.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 25 -Paragraph 11 -URI http://asc.fasb.org/extlink&oid=6482067&loc=d3e13145-158430 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 13 -Subparagraph a -Article 7 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03.13(a)(1)) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 60 -Paragraph 21-26 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. 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This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. false2Amortization of deferred acquisition costs57false 5us-gaap_InterestCreditedToPolicyholdersAccountBalancesus-gaap_truedebitdurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truefalsefalse92440009244USD$falsefalsefalse2truefalsefalse64310006431USD$falsefalsefalse3truefalsefalse3123500031235USD$falsefalsefalse4truefalsefalse2124300021243USD$falsefalsefalse5falsefalsefalse00falsefalsefalsexbrli:monetaryItemTypemonetaryInterest allocated to policyholders holding contracts under which the insurer must provide a guaranteed yield.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 225 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-04.6) -URI http://asc.fasb.org/extlink&oid=6879464&loc=d3e573970-122913 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 20 -Section 45 -Paragraph 2 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=6480726&loc=d3e6691-158385 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 97 -Paragraph 21 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. 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This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. false2Future policy benefits67false 5us-gaap_PolicyholderFundsus-gaap_truecreditinstantfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truefalsefalse137387000137387USD$falsefalsefalse2truefalsefalse128496000128496USD$falsefalsefalse3truefalsefalse137387000137387USD$falsefalsefalse4truefalsefalse128496000128496USD$falsefalsefalse5falsefalsefalse00falsefalsefalsexbrli:monetaryItemTypemonetaryThe total liability as of the balance sheet date of amounts due policy holders, excluding future policy benefits and claims, including unpaid policy dividends, retrospective refunds, and undistributed earnings on participating business.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03.13,14) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 false2Other policyholder liabilities68true 4us-gaap_IncomeStatementAbstractus-gaap_truenadurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1falsefalsefalse00falsefalsefalse2falsefalsefalse00falsefalsefalse3falsefalsefalse00falsefalsefalse4falsefalsefalse00falsefalsefalse5falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringfalse0Condensed Consolidated Income Statements:69false 5nwli_PremiumsEarnedAndPolicyChargesnwli_falsecreditdurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truefalsefalse59910005991USD$falsefalsefalse2truefalsefalse51620005162USD$falsefalsefalse3truefalsefalse1012500010125USD$falsefalsefalse4truefalsefalse1147400011474USD$falsefalsefalse5falsefalsefalse00falsefalsefalsexbrli:monetaryItemTypemonetaryPremiums earned and policy chargesNo definition available.false2Premiums and contract revenues70false 5us-gaap_NetInvestmentIncomeus-gaap_truecreditdurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truefalsefalse102805000102805USD$falsefalsefalse2truefalsefalse6187500061875USD$falsefalsefalse3truefalsefalse253183000253183USD$falsefalsefalse4truefalsefalse186264000186264USD$falsefalsefalse5falsefalsefalse00falsefalsefalsexbrli:monetaryItemTypemonetaryThe income earned from investments in securities and property, equipment and other capital assets. 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This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. false2Amortization of deferred acquisition costs75false 5us-gaap_InterestCreditedToPolicyholdersAccountBalancesus-gaap_truedebitdurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truefalsefalse5432600054326USD$falsefalsefalse2truefalsefalse1834300018343USD$falsefalsefalse3truefalsefalse165444000165444USD$falsefalsefalse4truefalsefalse9786100097861USD$falsefalsefalse5falsefalsefalse00falsefalsefalsexbrli:monetaryItemTypemonetaryInterest allocated to policyholders holding contracts under which the insurer must provide a guaranteed yield.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 225 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-04.6) -URI http://asc.fasb.org/extlink&oid=6879464&loc=d3e573970-122913 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 20 -Section 45 -Paragraph 2 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=6480726&loc=d3e6691-158385 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 97 -Paragraph 21 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. 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