SUMMARY OF INVESTMENTS (Fair Value of Investments) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
HELD-TO-MATURITY
Amortized Cost	$ 0	$ 150
Fair Value	0	150
AVAILABLE-FOR-SALE
Debt Securities, Available-for-sale, Amortized Cost	1,761,289	1,516,610
Available-for-sale, at fair value (amortized cost $150 in 2018 and $0 in 2017)	1,749,488	1,535,070
Fixed maturities
HELD-TO-MATURITY
Amortized Cost		150
Gross Unrealized Appreciation		0
Gross Unrealized Depreciation		0
Fair Value		150
AVAILABLE-FOR-SALE
Available-for-sale Securities, Amortized Cost Basis		1,516,610
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax		27,412
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax		8,952
Available-for-sale securities		1,535,070
Fixed maturities | Discontinued Operations
HELD-TO-MATURITY
Amortized Cost		34
Gross Unrealized Appreciation		0
Gross Unrealized Depreciation		0
Fair Value		34
AVAILABLE-FOR-SALE
Available-for-sale Securities, Amortized Cost Basis		1,412,291
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax		25,055
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax		7,321
Available-for-sale securities		1,430,025
Fixed maturities | Continuing and Discontinuing Operations
HELD-TO-MATURITY
Amortized Cost		184
Gross Unrealized Appreciation		0
Gross Unrealized Depreciation		0
Fair Value		184
AVAILABLE-FOR-SALE
Debt Securities, Available-for-sale, Amortized Cost	1,761,289
Fixed Maturity, Gross Unrealized Appreciation	11,844
Fixed Maturity, Gross Unrealized Depreciation	23,645
Available-for-sale, at fair value (amortized cost $150 in 2018 and $0 in 2017)	1,749,488
Available-for-sale Securities, Amortized Cost Basis		2,928,901
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax		52,467
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax		16,273
Available-for-sale securities		2,965,095
U.S. Treasury | Continuing and Discontinuing Operations
AVAILABLE-FOR-SALE
Debt Securities, Available-for-sale, Amortized Cost	27,632
Fixed Maturity, Gross Unrealized Appreciation	6
Fixed Maturity, Gross Unrealized Depreciation	220
Available-for-sale, at fair value (amortized cost $150 in 2018 and $0 in 2017)	27,418
Available-for-sale Securities, Amortized Cost Basis		17,073
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax		4
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax		186
Available-for-sale securities		16,891
U.S. government agency | Continuing and Discontinuing Operations
AVAILABLE-FOR-SALE
Debt Securities, Available-for-sale, Amortized Cost	215,535
Fixed Maturity, Gross Unrealized Appreciation	896
Fixed Maturity, Gross Unrealized Depreciation	1,749
Available-for-sale, at fair value (amortized cost $150 in 2018 and $0 in 2017)	214,682
Available-for-sale Securities, Amortized Cost Basis		121,574
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax		1,311
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax		717
Available-for-sale securities		122,168
General obligations | Midwest | Continuing and Discontinuing Operations
AVAILABLE-FOR-SALE
Debt Securities, Available-for-sale, Amortized Cost	94,806
Fixed Maturity, Gross Unrealized Appreciation	1,091
Fixed Maturity, Gross Unrealized Depreciation	685
Available-for-sale, at fair value (amortized cost $150 in 2018 and $0 in 2017)	95,212
Available-for-sale Securities, Amortized Cost Basis		107,689
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax		2,446
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax		439
Available-for-sale securities		109,696
General obligations | Northeast | Continuing and Discontinuing Operations
AVAILABLE-FOR-SALE
Debt Securities, Available-for-sale, Amortized Cost	37,326
Fixed Maturity, Gross Unrealized Appreciation	432
Fixed Maturity, Gross Unrealized Depreciation	103
Available-for-sale, at fair value (amortized cost $150 in 2018 and $0 in 2017)	37,655
Available-for-sale Securities, Amortized Cost Basis		47,477
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax		1,174
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax		10
Available-for-sale securities		48,641
General obligations | South | Continuing and Discontinuing Operations
AVAILABLE-FOR-SALE
Debt Securities, Available-for-sale, Amortized Cost	114,710
Fixed Maturity, Gross Unrealized Appreciation	754
Fixed Maturity, Gross Unrealized Depreciation	1,553
Available-for-sale, at fair value (amortized cost $150 in 2018 and $0 in 2017)	113,911
Available-for-sale Securities, Amortized Cost Basis		139,870
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax		2,462
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax		813
Available-for-sale securities		141,519
General obligations | West | Continuing and Discontinuing Operations
AVAILABLE-FOR-SALE
Debt Securities, Available-for-sale, Amortized Cost	107,787
Fixed Maturity, Gross Unrealized Appreciation	1,229
Fixed Maturity, Gross Unrealized Depreciation	1,175
Available-for-sale, at fair value (amortized cost $150 in 2018 and $0 in 2017)	107,841
Available-for-sale Securities, Amortized Cost Basis		111,123
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax		2,351
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax		463
Available-for-sale securities		113,011
Special revenue | Midwest | Continuing and Discontinuing Operations
AVAILABLE-FOR-SALE
Debt Securities, Available-for-sale, Amortized Cost	140,025
Fixed Maturity, Gross Unrealized Appreciation	1,609
Fixed Maturity, Gross Unrealized Depreciation	870
Available-for-sale, at fair value (amortized cost $150 in 2018 and $0 in 2017)	140,764
Available-for-sale Securities, Amortized Cost Basis		155,475
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax		3,620
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax		351
Available-for-sale securities		158,744
Special revenue | Northeast | Continuing and Discontinuing Operations
AVAILABLE-FOR-SALE
Debt Securities, Available-for-sale, Amortized Cost	62,737
Fixed Maturity, Gross Unrealized Appreciation	452
Fixed Maturity, Gross Unrealized Depreciation	1,241
Available-for-sale, at fair value (amortized cost $150 in 2018 and $0 in 2017)	61,948
Available-for-sale Securities, Amortized Cost Basis		79,028
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax		1,351
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax		619
Available-for-sale securities		79,760
Special revenue | South | Continuing and Discontinuing Operations
AVAILABLE-FOR-SALE
Debt Securities, Available-for-sale, Amortized Cost	237,848
Fixed Maturity, Gross Unrealized Appreciation	1,669
Fixed Maturity, Gross Unrealized Depreciation	3,708
Available-for-sale, at fair value (amortized cost $150 in 2018 and $0 in 2017)	235,809
Available-for-sale Securities, Amortized Cost Basis		260,145
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax		5,218
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax		1,851
Available-for-sale securities		263,512
Special revenue | West | Continuing and Discontinuing Operations
AVAILABLE-FOR-SALE
Debt Securities, Available-for-sale, Amortized Cost	143,829
Fixed Maturity, Gross Unrealized Appreciation	1,294
Fixed Maturity, Gross Unrealized Depreciation	2,203
Available-for-sale, at fair value (amortized cost $150 in 2018 and $0 in 2017)	142,920
Available-for-sale Securities, Amortized Cost Basis		156,576
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax		2,929
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax		1,198
Available-for-sale securities		158,307
Foreign bonds | Continuing and Discontinuing Operations
AVAILABLE-FOR-SALE
Debt Securities, Available-for-sale, Amortized Cost	9,698
Fixed Maturity, Gross Unrealized Appreciation	31
Fixed Maturity, Gross Unrealized Depreciation	13
Available-for-sale, at fair value (amortized cost $150 in 2018 and $0 in 2017)	9,716
Available-for-sale Securities, Amortized Cost Basis		51,361
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax		1,441
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax		49
Available-for-sale securities		52,753
Public utilities | Continuing and Discontinuing Operations
AVAILABLE-FOR-SALE
Debt Securities, Available-for-sale, Amortized Cost	56,808
Fixed Maturity, Gross Unrealized Appreciation	274
Fixed Maturity, Gross Unrealized Depreciation	1,023
Available-for-sale, at fair value (amortized cost $150 in 2018 and $0 in 2017)	56,059
Available-for-sale Securities, Amortized Cost Basis		206,028
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax		3,386
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax		270
Available-for-sale securities		209,144
Corporate bonds | Energy | Continuing and Discontinuing Operations
AVAILABLE-FOR-SALE
Debt Securities, Available-for-sale, Amortized Cost	28,909
Fixed Maturity, Gross Unrealized Appreciation	43
Fixed Maturity, Gross Unrealized Depreciation	304
Available-for-sale, at fair value (amortized cost $150 in 2018 and $0 in 2017)	28,648
Available-for-sale Securities, Amortized Cost Basis		93,191
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax		1,972
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax		110
Available-for-sale securities		95,053
Corporate bonds | Industrials | Continuing and Discontinuing Operations
AVAILABLE-FOR-SALE
Debt Securities, Available-for-sale, Amortized Cost	53,867
Fixed Maturity, Gross Unrealized Appreciation	124
Fixed Maturity, Gross Unrealized Depreciation	906
Available-for-sale, at fair value (amortized cost $150 in 2018 and $0 in 2017)	53,085
Available-for-sale Securities, Amortized Cost Basis		218,067
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax		3,881
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax		241
Available-for-sale securities		221,707
Corporate bonds | Consumer goods and services | Continuing and Discontinuing Operations
AVAILABLE-FOR-SALE
Debt Securities, Available-for-sale, Amortized Cost	54,323
Fixed Maturity, Gross Unrealized Appreciation	142
Fixed Maturity, Gross Unrealized Depreciation	819
Available-for-sale, at fair value (amortized cost $150 in 2018 and $0 in 2017)	53,646
Available-for-sale Securities, Amortized Cost Basis		183,253
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax		3,498
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax		494
Available-for-sale securities		186,257
Corporate bonds | Health care | Continuing and Discontinuing Operations
AVAILABLE-FOR-SALE
Debt Securities, Available-for-sale, Amortized Cost	16,721
Fixed Maturity, Gross Unrealized Appreciation	42
Fixed Maturity, Gross Unrealized Depreciation	105
Available-for-sale, at fair value (amortized cost $150 in 2018 and $0 in 2017)	16,658
Available-for-sale Securities, Amortized Cost Basis		74,125
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax		1,312
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax		29
Available-for-sale securities		75,408
Corporate bonds | Technology, media and telecommunications | Continuing and Discontinuing Operations
AVAILABLE-FOR-SALE
Debt Securities, Available-for-sale, Amortized Cost	26,819
Fixed Maturity, Gross Unrealized Appreciation	35
Fixed Maturity, Gross Unrealized Depreciation	678
Available-for-sale, at fair value (amortized cost $150 in 2018 and $0 in 2017)	26,176
Available-for-sale Securities, Amortized Cost Basis		146,853
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax		2,376
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax		250
Available-for-sale securities		148,979
Corporate bonds | Financial services | Continuing and Discontinuing Operations
HELD-TO-MATURITY
Amortized Cost		150
Gross Unrealized Appreciation		0
Gross Unrealized Depreciation		0
Fair Value		150
AVAILABLE-FOR-SALE
Debt Securities, Available-for-sale, Amortized Cost	81,286
Fixed Maturity, Gross Unrealized Appreciation	238
Fixed Maturity, Gross Unrealized Depreciation	2,175
Available-for-sale, at fair value (amortized cost $150 in 2018 and $0 in 2017)	79,349
Available-for-sale Securities, Amortized Cost Basis		277,824
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax		5,769
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax		442
Available-for-sale securities		283,151
Mortgage-backed securities | Continuing and Discontinuing Operations
HELD-TO-MATURITY
Amortized Cost		34
Gross Unrealized Appreciation		0
Gross Unrealized Depreciation		0
Fair Value		34
AVAILABLE-FOR-SALE
Debt Securities, Available-for-sale, Amortized Cost	7,642
Fixed Maturity, Gross Unrealized Appreciation	14
Fixed Maturity, Gross Unrealized Depreciation	232
Available-for-sale, at fair value (amortized cost $150 in 2018 and $0 in 2017)	7,424
Available-for-sale Securities, Amortized Cost Basis		13,828
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax		101
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax		238
Available-for-sale securities		13,691
Collateralized mortgage obligations | Government national mortgage association | Continuing and Discontinuing Operations
AVAILABLE-FOR-SALE
Debt Securities, Available-for-sale, Amortized Cost	78,055
Fixed Maturity, Gross Unrealized Appreciation	380
Fixed Maturity, Gross Unrealized Depreciation	1,734
Available-for-sale, at fair value (amortized cost $150 in 2018 and $0 in 2017)	76,701
Available-for-sale Securities, Amortized Cost Basis		157,836
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax		1,921
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax		2,274
Available-for-sale securities		157,483
Collateralized mortgage obligations | Federal home loan mortgage corporation | Continuing and Discontinuing Operations
AVAILABLE-FOR-SALE
Debt Securities, Available-for-sale, Amortized Cost	108,403
Fixed Maturity, Gross Unrealized Appreciation	524
Fixed Maturity, Gross Unrealized Depreciation	1,304
Available-for-sale, at fair value (amortized cost $150 in 2018 and $0 in 2017)	107,623
Available-for-sale Securities, Amortized Cost Basis		201,320
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax		1,879
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax		4,047
Available-for-sale securities		199,152
Collateralized mortgage obligations | Federal national mortgage association | Continuing and Discontinuing Operations
AVAILABLE-FOR-SALE
Debt Securities, Available-for-sale, Amortized Cost	53,267
Fixed Maturity, Gross Unrealized Appreciation	213
Fixed Maturity, Gross Unrealized Depreciation	732
Available-for-sale, at fair value (amortized cost $150 in 2018 and $0 in 2017)	52,748
Available-for-sale Securities, Amortized Cost Basis		104,903
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax		1,703
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax		1,174
Available-for-sale securities		105,432
Asset-backed securities | Continuing and Discontinuing Operations
AVAILABLE-FOR-SALE
Debt Securities, Available-for-sale, Amortized Cost	3,256
Fixed Maturity, Gross Unrealized Appreciation	352
Fixed Maturity, Gross Unrealized Depreciation	113
Available-for-sale, at fair value (amortized cost $150 in 2018 and $0 in 2017)	$ 3,495
Available-for-sale Securities, Amortized Cost Basis		4,282
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax		362
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax		8
Available-for-sale securities		$ 4,636