SUMMARY OF INVESTMENTS (Fair Value of Investments) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
AVAILABLE-FOR-SALE
Cost or Amortized Cost	$ 1,720,291	$ 1,659,760
Fair Value	1,825,438	1,719,607
Allowance for Credit Losses	5	0
Fixed maturities
AVAILABLE-FOR-SALE
Cost or Amortized Cost	1,720,291	1,659,760
Gross Unrealized Appreciation	107,003	60,639
Gross Unrealized Depreciation	1,851	792
Fair Value	1,825,443	1,719,607
Allowance for Credit Losses	5
U.S. Treasury
AVAILABLE-FOR-SALE
Cost or Amortized Cost	149,481	69,300
Gross Unrealized Appreciation	482	203
Gross Unrealized Depreciation	25	12
Fair Value	149,938	69,491
Allowance for Credit Losses	0
U.S. government agency
AVAILABLE-FOR-SALE
Cost or Amortized Cost	60,502	97,962
Gross Unrealized Appreciation	4,016	2,344
Gross Unrealized Depreciation	0	104
Fair Value	64,518	100,202
Allowance for Credit Losses	0
General obligations \| Midwest
AVAILABLE-FOR-SALE
Cost or Amortized Cost	77,933	85,607
Gross Unrealized Appreciation	4,047	2,987
Gross Unrealized Depreciation	0	0
Fair Value	81,980	88,594
Allowance for Credit Losses	0
General obligations \| Northeast
AVAILABLE-FOR-SALE
Cost or Amortized Cost	29,071	30,120
Gross Unrealized Appreciation	1,379	1,150
Gross Unrealized Depreciation	0	0
Fair Value	30,450	31,270
Allowance for Credit Losses	0
General obligations \| South
AVAILABLE-FOR-SALE
Cost or Amortized Cost	104,522	111,688
Gross Unrealized Appreciation	5,448	3,515
Gross Unrealized Depreciation	0	0
Fair Value	109,970	115,203
Allowance for Credit Losses	0
General obligations \| West
AVAILABLE-FOR-SALE
Cost or Amortized Cost	102,590	105,569
Gross Unrealized Appreciation	7,431	4,748
Gross Unrealized Depreciation	0	0
Fair Value	110,021	110,317
Allowance for Credit Losses	0
Special revenue \| Midwest
AVAILABLE-FOR-SALE
Cost or Amortized Cost	115,956	133,717
Gross Unrealized Appreciation	9,142	6,175
Gross Unrealized Depreciation	0	0
Fair Value	125,098	139,892
Allowance for Credit Losses	0
Special revenue \| Northeast
AVAILABLE-FOR-SALE
Cost or Amortized Cost	56,317	58,665
Gross Unrealized Appreciation	4,759	2,878
Gross Unrealized Depreciation	0	0
Fair Value	61,076	61,543
Allowance for Credit Losses	0
Special revenue \| South
AVAILABLE-FOR-SALE
Cost or Amortized Cost	208,739	224,214
Gross Unrealized Appreciation	17,967	10,452
Gross Unrealized Depreciation	0	0
Fair Value	226,706	234,666
Allowance for Credit Losses	0
Special revenue \| West
AVAILABLE-FOR-SALE
Cost or Amortized Cost	129,417	138,557
Gross Unrealized Appreciation	9,982	6,287
Gross Unrealized Depreciation	0	0
Fair Value	139,399	144,844
Allowance for Credit Losses	0
Foreign bonds
AVAILABLE-FOR-SALE
Cost or Amortized Cost	27,799	4,936
Gross Unrealized Appreciation	1,805	181
Gross Unrealized Depreciation	2	0
Fair Value	29,602	5,117
Allowance for Credit Losses	0
Public utilities
AVAILABLE-FOR-SALE
Cost or Amortized Cost	76,114	60,950
Gross Unrealized Appreciation	7,388	2,701
Gross Unrealized Depreciation	0	0
Fair Value	83,502	63,651
Allowance for Credit Losses	0
Corporate bonds \| Energy
AVAILABLE-FOR-SALE
Cost or Amortized Cost	22,441	28,695
Gross Unrealized Appreciation	2,895	1,429
Gross Unrealized Depreciation	0	0
Fair Value	25,336	30,124
Allowance for Credit Losses	0
Corporate bonds \| Industrials
AVAILABLE-FOR-SALE
Cost or Amortized Cost	39,513	52,249
Gross Unrealized Appreciation	3,744	1,766
Gross Unrealized Depreciation	0	0
Fair Value	43,257	54,015
Allowance for Credit Losses	0
Corporate bonds \| Consumer goods and services
AVAILABLE-FOR-SALE
Cost or Amortized Cost	46,521	47,131
Gross Unrealized Appreciation	4,046	2,335
Gross Unrealized Depreciation	0	0
Fair Value	50,567	49,466
Allowance for Credit Losses	0
Corporate bonds \| Health care
AVAILABLE-FOR-SALE
Cost or Amortized Cost	6,678	8,998
Gross Unrealized Appreciation	898	482
Gross Unrealized Depreciation	0	0
Fair Value	7,576	9,480
Allowance for Credit Losses	0
Corporate bonds \| Technology, media and telecommunications
AVAILABLE-FOR-SALE
Cost or Amortized Cost	37,270	25,931
Gross Unrealized Appreciation	4,381	1,739
Gross Unrealized Depreciation	15	0
Fair Value	41,636	27,670
Allowance for Credit Losses	0
Corporate bonds \| Financial services
AVAILABLE-FOR-SALE
Cost or Amortized Cost	93,736	96,613
Gross Unrealized Appreciation	7,564	3,870
Gross Unrealized Depreciation	269	230
Fair Value	101,031	100,253
Allowance for Credit Losses	5
Mortgage-backed securities
AVAILABLE-FOR-SALE
Cost or Amortized Cost	20,305	6,250
Gross Unrealized Appreciation	326	127
Gross Unrealized Depreciation	54	21
Fair Value	20,577	6,356
Allowance for Credit Losses	0
Collateralized mortgage obligations \| Government national mortgage association
AVAILABLE-FOR-SALE
Cost or Amortized Cost	81,758	78,400
Gross Unrealized Appreciation	4,439	2,053
Gross Unrealized Depreciation	45	97
Fair Value	86,152	80,356
Allowance for Credit Losses	0
Collateralized mortgage obligations \| Federal home loan mortgage corporation
AVAILABLE-FOR-SALE
Cost or Amortized Cost	151,362	123,572
Gross Unrealized Appreciation	2,239	1,150
Gross Unrealized Depreciation	758	220
Fair Value	152,843	124,502
Allowance for Credit Losses	0
Collateralized mortgage obligations \| Federal national mortgage association
AVAILABLE-FOR-SALE
Cost or Amortized Cost	81,952	70,322
Gross Unrealized Appreciation	2,013	1,631
Gross Unrealized Depreciation	683	108
Fair Value	83,282	71,845
Allowance for Credit Losses	0
Asset-backed securities
AVAILABLE-FOR-SALE
Cost or Amortized Cost	314	314
Gross Unrealized Appreciation	612	436
Gross Unrealized Depreciation	0	0
Fair Value	926	$ 750
Allowance for Credit Losses	0
Carrying Value \| Fixed maturities
AVAILABLE-FOR-SALE
Fair Value	1,825,438
Carrying Value \| U.S. Treasury
AVAILABLE-FOR-SALE
Fair Value	149,938
Carrying Value \| U.S. government agency
AVAILABLE-FOR-SALE
Fair Value	64,518
Carrying Value \| General obligations \| Midwest
AVAILABLE-FOR-SALE
Fair Value	81,980
Carrying Value \| General obligations \| Northeast
AVAILABLE-FOR-SALE
Fair Value	30,450
Carrying Value \| General obligations \| South
AVAILABLE-FOR-SALE
Fair Value	109,970
Carrying Value \| General obligations \| West
AVAILABLE-FOR-SALE
Fair Value	110,021
Carrying Value \| Special revenue \| Midwest
AVAILABLE-FOR-SALE
Fair Value	125,098
Carrying Value \| Special revenue \| Northeast
AVAILABLE-FOR-SALE
Fair Value	61,076
Carrying Value \| Special revenue \| South
AVAILABLE-FOR-SALE
Fair Value	226,706
Carrying Value \| Special revenue \| West
AVAILABLE-FOR-SALE
Fair Value	139,399
Carrying Value \| Foreign bonds
AVAILABLE-FOR-SALE
Fair Value	29,602
Carrying Value \| Public utilities
AVAILABLE-FOR-SALE
Fair Value	83,502
Carrying Value \| Corporate bonds \| Energy
AVAILABLE-FOR-SALE
Fair Value	25,336
Carrying Value \| Corporate bonds \| Industrials
AVAILABLE-FOR-SALE
Fair Value	43,257
Carrying Value \| Corporate bonds \| Consumer goods and services
AVAILABLE-FOR-SALE
Fair Value	50,567
Carrying Value \| Corporate bonds \| Health care
AVAILABLE-FOR-SALE
Fair Value	7,576
Carrying Value \| Corporate bonds \| Technology, media and telecommunications
AVAILABLE-FOR-SALE
Fair Value	41,636
Carrying Value \| Corporate bonds \| Financial services
AVAILABLE-FOR-SALE
Fair Value	101,026
Carrying Value \| Mortgage-backed securities
AVAILABLE-FOR-SALE
Fair Value	20,577
Carrying Value \| Collateralized mortgage obligations \| Government national mortgage association
AVAILABLE-FOR-SALE
Fair Value	86,152
Carrying Value \| Collateralized mortgage obligations \| Federal home loan mortgage corporation
AVAILABLE-FOR-SALE
Fair Value	152,843
Carrying Value \| Collateralized mortgage obligations \| Federal national mortgage association
AVAILABLE-FOR-SALE
Fair Value	83,282
Carrying Value \| Asset-backed securities
AVAILABLE-FOR-SALE
Fair Value	$ 926

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).

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=121645371&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=121645371&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=121645371&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=121558606&loc=SL82898722-210454

+ Details

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

- References

No definition available.

+ Details

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

- 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 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(6))
-URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878

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=121558606&loc=SL82898722-210454

Reference 3: 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=121553693&loc=d3e26610-111562

Reference 4: 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=121645371&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 allowance for credit loss 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://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 50
-Paragraph 9
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=121582814&loc=SL82922900-210455

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 50
-Paragraph 9
-Subparagraph (i)
-URI http://asc.fasb.org/extlink&oid=121582814&loc=SL82922900-210455

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (aaa)
-URI http://asc.fasb.org/extlink&oid=121645371&loc=d3e27161-111563

Reference 4: 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=121558606&loc=SL82898722-210454

+ Details

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