INVESTMENTS (Available-for-Sale Securities) (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Fixed maturities, Amortized Cost	$ 101,828	$ 97,102
Fixed maturities, Gross Unrealized Gains	3,468	3,494
Fixed maturities, Gross Unrealized Losses	2,766	336
Fixed maturities, Fair Value	102,530	100,260
Equity securities, Amortized Cost	2,127	2,127
Equity securities, Gross Unrealized Gains	2,607	3,176
Equity securities, Gross Unrealized Losses	30	0
Equity securities, Fair Value	4,704	5,303
Amortized Cost	103,955	99,229
Gross Unrealized Gains	6,075	6,670
Gross Unrealized Losses	2,796	336
Fair Value	107,234	105,563
U.S. Government corporations and agencies
Debt Securities, Available-for-sale [Line Items]
Fixed maturities, Amortized Cost	4,569	4,131
Fixed maturities, Gross Unrealized Gains	326	150
Fixed maturities, Gross Unrealized Losses	0	0
Fixed maturities, Fair Value	4,895	4,281
Agency mortgage backed securities
Debt Securities, Available-for-sale [Line Items]
Fixed maturities, Amortized Cost	33,437	32,283
Fixed maturities, Gross Unrealized Gains	1,569	861
Fixed maturities, Gross Unrealized Losses	19	157
Fixed maturities, Fair Value	34,987	32,987
Asset backed securities
Debt Securities, Available-for-sale [Line Items]
Fixed maturities, Amortized Cost	10,195	10,307
Fixed maturities, Gross Unrealized Gains	37	71
Fixed maturities, Gross Unrealized Losses	962	104
Fixed maturities, Fair Value	9,270	10,274
Private label mortgage backed securities
Debt Securities, Available-for-sale [Line Items]
Fixed maturities, Amortized Cost	8,255	6,815
Fixed maturities, Gross Unrealized Gains	115	441
Fixed maturities, Gross Unrealized Losses	50	4
Fixed maturities, Fair Value	8,320	7,252
Corporate bonds
Debt Securities, Available-for-sale [Line Items]
Fixed maturities, Amortized Cost	38,365	36,074
Fixed maturities, Gross Unrealized Gains	1,170	1,816
Fixed maturities, Gross Unrealized Losses	1,721	70
Fixed maturities, Fair Value	37,814	37,820
States, municipalities and political subdivisions
Debt Securities, Available-for-sale [Line Items]
Fixed maturities, Amortized Cost	6,178	6,669
Fixed maturities, Gross Unrealized Gains	153	109
Fixed maturities, Gross Unrealized Losses	14	1
Fixed maturities, Fair Value	6,317	6,777
Foreign governments
Debt Securities, Available-for-sale [Line Items]
Fixed maturities, Amortized Cost	829	823
Fixed maturities, Gross Unrealized Gains	98	46
Fixed maturities, Gross Unrealized Losses	0	0
Fixed maturities, Fair Value	$ 927	$ 869

Available-for-sale Debt and Equity Securities, Accumulated Gross Unrealized Gain, before Tax

No definition available.

Name:	nsec_AvailableforsaleDebtandEquitySecuritiesAccumulatedGrossUnrealizedGainbeforeTax
Namespace Prefix:	nsec_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Available-for-sale Debt and Equity Securities, Accumulated Gross Unrealized Loss, before Tax

+ References

No definition available.

+ Details

Name:	nsec_AvailableforsaleDebtandEquitySecuritiesAccumulatedGrossUnrealizedLossbeforeTax
Namespace Prefix:	nsec_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Available-for-sale Debt and Equity Securities, Amortized Cost Basis

+ References

No definition available.

+ Details

Name:	nsec_AvailableforsaleDebtandEquitySecuritiesAmortizedCostBasis
Namespace Prefix:	nsec_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Available-for-sale Securities, Debt and Equity Securities

+ References

No definition available.

+ Details

Name:	nsec_AvailableforsaleSecuritiesDebtandEquitySecurities
Namespace Prefix:	nsec_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27161-111563

+ Details

Name:	us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27161-111563

+ Details

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

- Definition

Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27161-111563

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=118942338&loc=SL82898722-210454

+ Details

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

- Definition

Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in equity securities classified as available-for-sale.

+ References

No definition available.

+ Details

Name:	us-gaap_AvailableForSaleEquitySecuritiesAccumulatedGrossUnrealizedGainBeforeTax
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in equity securities classified as available-for-sale.

+ References

No definition available.

+ Details

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

- Definition

This item represents the cost of equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments for other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

+ References

No definition available.

+ Details

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

- Definition

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=118942338&loc=SL82898722-210454

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=118954083&loc=d3e26610-111562

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (aa)
-URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27161-111563

+ Details

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

- Definition

Amount of equity securities categorized neither as held-to-maturity nor as trading.

+ References

No definition available.

+ Details

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

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

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_USGovernmentAgenciesDebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_AssetBackedSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_CorporateBondSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_USStatesAndPoliticalSubdivisionsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_ForeignGovernmentDebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: