SUMMARY OF INVESTMENTS (Investments in Unrealized Loss Position) (Details) $ in Thousands	Dec. 31, 2017 USD ($) issue	Dec. 31, 2016 USD ($) issue
Continuing and Discontinuing Operations
Number of Issues
Less than 12 months | issue	169	567
12 months or longer | issue	183	55
Fair Value
Less than 12 months	$ 414,666	$ 1,060,938
12 months or longer	471,075	53,798
Total	885,741	1,114,736
Gross Unrealized Depreciation
Less than 12 months	3,489	32,167
12 months or longer	13,400	2,598
Total	$ 16,889	$ 34,765
U.S. Treasury | Continuing and Discontinuing Operations
Number of Issues
Less than 12 months | issue	5	9
12 months or longer | issue	2	0
Fair Value
Less than 12 months	$ 10,370	$ 10,800
12 months or longer	5,765	0
Total	16,135	10,800
Gross Unrealized Depreciation
Less than 12 months	67	108
12 months or longer	119	0
Total	$ 186	$ 108
U.S. government agency | Continuing and Discontinuing Operations
Number of Issues
Less than 12 months | issue	11	10
12 months or longer | issue	5	0
Fair Value
Less than 12 months	$ 64,842	$ 36,593
12 months or longer	19,372	0
Total	84,214	36,593
Gross Unrealized Depreciation
Less than 12 months	390	540
12 months or longer	327	0
Total	$ 717	$ 540
Fixed maturities
Number of Issues
Less than 12 months | issue	88	404
12 months or longer | issue	112	12
Fair Value
Less than 12 months	$ 232,489	$ 654,235
12 months or longer	302,815	6,288
Total	535,304	660,523
Gross Unrealized Depreciation
Less than 12 months	1,791	23,359
12 months or longer	7,161	315
Total	$ 8,952	$ 23,674
Fixed maturities | Discontinued Operations
Number of Issues
Less than 12 months | issue	74	150
12 months or longer | issue	61	21
Fair Value
Less than 12 months	$ 180,891	$ 406,342
12 months or longer	167,625	46,790
Total	348,516	453,132
Gross Unrealized Depreciation
Less than 12 months	1,415	8,745
12 months or longer	5,906	1,800
Total	$ 7,321	$ 10,545
Fixed maturities | Continuing and Discontinuing Operations
Number of Issues
Less than 12 months | issue	162	554
12 months or longer | issue	173	33
Fair Value
Less than 12 months	$ 413,380	$ 1,060,577
12 months or longer	470,440	53,078
Total	883,820	1,113,655
Gross Unrealized Depreciation
Less than 12 months	3,206	32,104
12 months or longer	13,067	2,115
Total	$ 16,273	$ 34,219
General obligations | Midwest | Continuing and Discontinuing Operations
Number of Issues
Less than 12 months | issue	2	27
12 months or longer | issue	3	0
Fair Value
Less than 12 months	$ 2,177	$ 40,545
12 months or longer	19,729	0
Total	21,906	40,545
Gross Unrealized Depreciation
Less than 12 months	8	1,412
12 months or longer	431	0
Total	$ 439	$ 1,412
General obligations | Northeast | Continuing and Discontinuing Operations
Number of Issues
Less than 12 months | issue	0	9
12 months or longer | issue	1	0
Fair Value
Less than 12 months	$ 0	$ 9,874
12 months or longer	3,644	0
Total	3,644	9,874
Gross Unrealized Depreciation
Less than 12 months	0	231
12 months or longer	10	0
Total	$ 10	$ 231
General obligations | South | Continuing and Discontinuing Operations
Number of Issues
Less than 12 months | issue	3	37
12 months or longer | issue	11	0
Fair Value
Less than 12 months	$ 7,959	$ 53,699
12 months or longer	29,545	0
Total	37,504	53,699
Gross Unrealized Depreciation
Less than 12 months	32	2,355
12 months or longer	781	0
Total	$ 813	$ 2,355
General obligations | West | Continuing and Discontinuing Operations
Number of Issues
Less than 12 months | issue	2	30
12 months or longer | issue	8	0
Fair Value
Less than 12 months	$ 5,944	$ 55,265
12 months or longer	25,755	0
Total	31,699	55,265
Gross Unrealized Depreciation
Less than 12 months	18	2,173
12 months or longer	445	0
Total	$ 463	$ 2,173
Special revenue | Midwest | Continuing and Discontinuing Operations
Number of Issues
Less than 12 months | issue	2	41
12 months or longer | issue	7	0
Fair Value
Less than 12 months	$ 3,486	$ 62,937
12 months or longer	19,130	0
Total	22,616	62,937
Gross Unrealized Depreciation
Less than 12 months	15	1,433
12 months or longer	336	0
Total	$ 351	$ 1,433
Special revenue | Northeast | Continuing and Discontinuing Operations
Number of Issues
Less than 12 months | issue	1	22
12 months or longer | issue	11	0
Fair Value
Less than 12 months	$ 4,471	$ 54,993
12 months or longer	28,476	0
Total	32,947	54,993
Gross Unrealized Depreciation
Less than 12 months	37	2,624
12 months or longer	582	0
Total	$ 619	$ 2,624
Special revenue | South | Continuing and Discontinuing Operations
Number of Issues
Less than 12 months | issue	8	79
12 months or longer | issue	27	0
Fair Value
Less than 12 months	$ 7,749	$ 152,979
12 months or longer	69,917	0
Total	77,666	152,979
Gross Unrealized Depreciation
Less than 12 months	107	6,791
12 months or longer	1,744	0
Total	$ 1,851	$ 6,791
Special revenue | West | Continuing and Discontinuing Operations
Number of Issues
Less than 12 months | issue	3	44
12 months or longer | issue	22	0
Fair Value
Less than 12 months	$ 5,424	$ 81,676
12 months or longer	56,753	0
Total	62,177	81,676
Gross Unrealized Depreciation
Less than 12 months	16	4,052
12 months or longer	1,182	0
Total	$ 1,198	$ 4,052
Foreign bonds | Continuing and Discontinuing Operations
Number of Issues
Less than 12 months | issue	1
12 months or longer | issue	0
Fair Value
Less than 12 months	$ 857
12 months or longer	0
Total	857
Gross Unrealized Depreciation
Less than 12 months	49
12 months or longer	0
Total	$ 49
Public utilities | Continuing and Discontinuing Operations
Number of Issues
Less than 12 months | issue	8	20
12 months or longer | issue	5	2
Fair Value
Less than 12 months	$ 19,186	$ 38,511
12 months or longer	8,446	2,122
Total	27,632	40,633
Gross Unrealized Depreciation
Less than 12 months	79	423
12 months or longer	191	24
Total	$ 270	$ 447
Corporate bonds | Financial services | Continuing and Discontinuing Operations
Number of Issues
Less than 12 months | issue	22	37
12 months or longer | issue	4	0
Fair Value
Less than 12 months	$ 50,144	$ 75,286
12 months or longer	11,389	0
Total	61,533	75,286
Gross Unrealized Depreciation
Less than 12 months	256	1,358
12 months or longer	186	0
Total	$ 442	$ 1,358
Corporate bonds | Energy | Continuing and Discontinuing Operations
Number of Issues
Less than 12 months | issue	1	8
12 months or longer | issue	1	3
Fair Value
Less than 12 months	$ 2,236	$ 15,938
12 months or longer	1,606	8,232
Total	3,842	24,170
Gross Unrealized Depreciation
Less than 12 months	13	313
12 months or longer	97	106
Total	$ 110	$ 419
Corporate bonds | Industrials | Continuing and Discontinuing Operations
Number of Issues
Less than 12 months | issue	10	24
12 months or longer | issue	2	3
Fair Value
Less than 12 months	$ 27,773	$ 42,854
12 months or longer	4,275	5,641
Total	32,048	48,495
Gross Unrealized Depreciation
Less than 12 months	146	596
12 months or longer	95	386
Total	$ 241	$ 982
Corporate bonds | Consumer goods and services | Continuing and Discontinuing Operations
Number of Issues
Less than 12 months | issue	14	11
12 months or longer | issue	3	0
Fair Value
Less than 12 months	$ 32,781	$ 21,059
12 months or longer	6,813	0
Total	39,594	21,059
Gross Unrealized Depreciation
Less than 12 months	248	295
12 months or longer	246	0
Total	$ 494	$ 295
Corporate bonds | Health care | Continuing and Discontinuing Operations
Number of Issues
Less than 12 months | issue	4	9
12 months or longer | issue	0	0
Fair Value
Less than 12 months	$ 9,947	$ 20,918
12 months or longer	0	0
Total	9,947	20,918
Gross Unrealized Depreciation
Less than 12 months	29	151
12 months or longer	0	0
Total	$ 29	$ 151
Corporate bonds | Technology, media and telecommunications | Continuing and Discontinuing Operations
Number of Issues
Less than 12 months | issue	12	16
12 months or longer | issue	3	3
Fair Value
Less than 12 months	$ 35,319	$ 41,230
12 months or longer	10,413	10,241
Total	45,732	51,471
Gross Unrealized Depreciation
Less than 12 months	122	516
12 months or longer	128	303
Total	$ 250	$ 819
Mortgage-backed securities | Continuing and Discontinuing Operations
Number of Issues
Less than 12 months | issue	10	16
12 months or longer | issue	10	5
Fair Value
Less than 12 months	$ 2,458	$ 9,611
12 months or longer	6,641	1,198
Total	9,099	10,809
Gross Unrealized Depreciation
Less than 12 months	18	187
12 months or longer	220	54
Total	$ 238	$ 241
Collateralized mortgage obligations | Government national mortgage association | Continuing and Discontinuing Operations
Number of Issues
Less than 12 months | issue	20	36
12 months or longer | issue	17	9
Fair Value
Less than 12 months	$ 49,764	$ 82,430
12 months or longer	46,969	13,603
Total	96,733	96,033
Gross Unrealized Depreciation
Less than 12 months	629	2,261
12 months or longer	1,645	505
Total	$ 2,274	$ 2,766
Collateralized mortgage obligations | Federal home loan mortgage corporation | Continuing and Discontinuing Operations
Number of Issues
Less than 12 months | issue	11	41
12 months or longer | issue	20	3
Fair Value
Less than 12 months	$ 37,543	$ 105,775
12 months or longer	75,679	5,141
Total	113,222	110,916
Gross Unrealized Depreciation
Less than 12 months	577	3,165
12 months or longer	3,470	241
Total	$ 4,047	$ 3,406
Collateralized mortgage obligations | Federal national mortgage association | Continuing and Discontinuing Operations
Number of Issues
Less than 12 months | issue	11	27
12 months or longer | issue	11	4
Fair Value
Less than 12 months	$ 31,958	$ 46,633
12 months or longer	20,123	4,341
Total	52,081	50,974
Gross Unrealized Depreciation
Less than 12 months	342	1,091
12 months or longer	832	243
Total	$ 1,174	$ 1,334
Asset-backed securities | Continuing and Discontinuing Operations
Number of Issues
Less than 12 months | issue	1	1
12 months or longer | issue	0	1
Fair Value
Less than 12 months	$ 992	$ 971
12 months or longer	0	2,559
Total	992	3,530
Gross Unrealized Depreciation
Less than 12 months	8	29
12 months or longer	0	253
Total	$ 8	$ 282
Equity securities
Number of Issues
Less than 12 months | issue	5	12
12 months or longer | issue	6	17
Fair Value
Less than 12 months	$ 1,129	$ 351
12 months or longer	385	477
Total	1,514	828
Gross Unrealized Depreciation
Less than 12 months	236	62
12 months or longer	303	254
Total	$ 539	$ 316
Equity securities | Discontinued Operations
Number of Issues
Less than 12 months | issue	2	1
12 months or longer | issue	4	5
Fair Value
Less than 12 months	$ 157	$ 10
12 months or longer	250	243
Total	407	253
Gross Unrealized Depreciation
Less than 12 months	47	1
12 months or longer	30	229
Total	$ 77	$ 230
Equity securities | Continuing and Discontinuing Operations
Number of Issues
Less than 12 months | issue	7	13
12 months or longer | issue	10	22
Fair Value
Less than 12 months	$ 1,286	$ 361
12 months or longer	635	720
Total	1,921	1,081
Gross Unrealized Depreciation
Less than 12 months	283	63
12 months or longer	333	483
Total	$ 616	$ 546
Common stock | Financial services | Continuing and Discontinuing Operations
Number of Issues
Less than 12 months | issue	2	3
12 months or longer | issue	1	2
Fair Value
Less than 12 months	$ 193	$ 53
12 months or longer	9	150
Total	202	203
Gross Unrealized Depreciation
Less than 12 months	55	3
12 months or longer	12	64
Total	$ 67	$ 67
Common stock | Public utilities | Continuing and Discontinuing Operations
Number of Issues
Less than 12 months | issue	0	0
12 months or longer | issue	1	3
Fair Value
Less than 12 months	$ 0	$ 0
12 months or longer	278	120
Total	278	120
Gross Unrealized Depreciation
Less than 12 months	0	0
12 months or longer	30	188
Total	$ 30	$ 188
Common stock | Energy | Continuing and Discontinuing Operations
Number of Issues
Less than 12 months | issue	2	0
12 months or longer | issue	0	1
Fair Value
Less than 12 months	$ 528	$ 0
12 months or longer	0	163
Total	528	163
Gross Unrealized Depreciation
Less than 12 months	120	0
12 months or longer	0	22
Total	$ 120	$ 22
Common stock | Industrials | Continuing and Discontinuing Operations
Number of Issues
Less than 12 months | issue	1	0
12 months or longer | issue	5	6
Fair Value
Less than 12 months	$ 99	$ 0
12 months or longer	193	239
Total	292	239
Gross Unrealized Depreciation
Less than 12 months	13	0
12 months or longer	107	173
Total	$ 120	$ 173
Common stock | Consumer goods and services | Continuing and Discontinuing Operations
Number of Issues
Less than 12 months | issue	0	3
12 months or longer | issue	2	2
Fair Value
Less than 12 months	$ 0	$ 282
12 months or longer	151	15
Total	151	297
Gross Unrealized Depreciation
Less than 12 months	0	55
12 months or longer	164	3
Total	$ 164	$ 58
Common stock | Technology, media and telecommunications | Continuing and Discontinuing Operations
Number of Issues
Less than 12 months | issue	2	7
12 months or longer | issue	1	8
Fair Value
Less than 12 months	$ 466	$ 26
12 months or longer	4	33
Total	470	59
Gross Unrealized Depreciation
Less than 12 months	95	5
12 months or longer	20	33
Total	$ 115	$ 38