LOSS AND LOSS ADJUSTMENT EXPENSE RESERVES Loss development tables (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008
Claims Development [Line Items]
Short-duration Insurance Contracts, Liability for Unpaid Claims and Claims Adjustment Expense, Accumulated Unallocated Claim Adjustment Expense	$ 4,307,000	$ 3,615,000
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net	430,614,000	300,322,000
Loss and loss adjustment expenses recoverable	29,459,000	2,704,000	$ 3,368,000	$ 11,523,000
Liability for Claims and Claims Adjustment Expense	$ 464,380,000	306,641,000	305,997,000	264,243,000
Short-duration Insurance Contracts, Claim Frequency, Impracticable	As a reinsurance entity, the Company does not consistently receive detailed claims frequency information or claims counts, from ceding insurers and third party claim handlers. Due to the nature of the reinsurance contracts, the underlying insured reports claims to the insurer who cedes losses to the Company. The Company is contractually obligated to reimburse the ceding insurer for its share of the losses. While the Company has the right to conduct audits of the ceding insurer’s claims files, the insurer is generally not obligated to provide detailed listing of claims counts or other claims frequency information to the Company. Therefore it is impracticable for the Company to present the cumulative number of reported claims by accident year.
Health
Claims Development [Line Items]
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net	$ 22,181,000	18,993,000
Loss and loss adjustment expenses recoverable	0	0	0	0
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	289,848,000
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net, Not Separately Presented	0
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	312,028,000
Liability for Claims and Claims Adjustment Expense	22,181,000	18,993,000	21,533,000	14,137,000
Frequency - non-health
Claims Development [Line Items]
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net	325,021,000	239,151,000
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	1,949,728,000
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net, Not Separately Presented	0
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	$ 2,274,750,000
Short-duration Insurance Contracts, Historical Claims Duration, Year One	37.30%
Short-duration Insurance Contracts, Historical Claims Duration, Year Two	30.50%
Short-duration Insurance Contracts, Historical Claims Duration, Year Three	9.50%
Short-duration Insurance Contracts, Historical Claims Duration, Year Four	5.70%
Short-duration Insurance Contracts, Historical Claims Duration, Year Five	5.00%
Short-duration Insurance Contracts, Historical Claims Duration, Year Six	6.80%
Short-duration Insurance Contracts, Historical Claims Duration, Year Seven	2.90%
Short-duration Insurance Contracts, Historical Claims Duration, Year Eight	1.90%
Short-duration Insurance Contracts, Historical Claims Duration, Year Nine	0.30%
Short-duration Insurance Contracts, Historical Claims Duration, Year Ten	0.10%
Severity
Claims Development [Line Items]
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net	$ 83,412,000	42,178,000
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	64,747,000
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net, Not Separately Presented	2,486,000
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	$ 145,671,000
Short-duration Insurance Contracts, Historical Claims Duration, Year One	3.10%
Short-duration Insurance Contracts, Historical Claims Duration, Year Two	11.80%
Short-duration Insurance Contracts, Historical Claims Duration, Year Three	9.50%
Short-duration Insurance Contracts, Historical Claims Duration, Year Four	8.50%
Short-duration Insurance Contracts, Historical Claims Duration, Year Five	18.00%
Short-duration Insurance Contracts, Historical Claims Duration, Year Six	4.00%
Short-duration Insurance Contracts, Historical Claims Duration, Year Seven	10.10%
Short-duration Insurance Contracts, Historical Claims Duration, Year Eight	0.80%
Short-duration Insurance Contracts, Historical Claims Duration, Year Nine	16.10%
Short-duration Insurance Contracts, Historical Claims Duration, Year Ten	18.10%
Short-duration Insurance Contracts, Accident Year 2008 | Health
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	$ 11,247,000	11,247,000	11,247,000	11,249,000	$ 11,249,000	$ 11,415,000	$ 11,277,000	$ 11,294,000	$ 10,890,000	$ 4,199,000
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	0
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	11,247,000	11,279,000	11,247,000	11,249,000	11,249,000	12,150,000	11,361,000	11,432,000	11,677,000	10,593,000
Short-duration Insurance Contracts, Accident Year 2008 | Frequency - non-health
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	41,752,000	41,707,000	41,310,000	41,190,000	40,269,000	39,151,000	36,587,000	31,686,000	25,145,000	10,345,000
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	33,000
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	41,785,000	41,707,000	42,078,000	41,620,000	40,518,000	40,523,000	38,669,000	35,893,000	34,675,000	38,126,000
Short-duration Insurance Contracts, Accident Year 2008 | Severity
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	15,402,000	15,243,000	10,504,000	10,356,000	10,356,000	10,320,000	6,391,000	3,148,000	0	0
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	4,810,000
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	20,212,000	20,212,000	17,843,000	19,582,000	19,583,000	17,469,000	18,028,000	18,026,000	19,329,000	16,466,000
Short-duration Insurance Contracts, Accident Year 2009 | Health
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	23,401,000	23,401,000	23,401,000	23,402,000	23,402,000	23,402,000	23,392,000	23,088,000	8,617,000	0
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	0
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	23,401,000	23,401,000	23,401,000	23,402,000	23,402,000	23,402,000	23,393,000	23,884,000	24,905,000	0
Short-duration Insurance Contracts, Accident Year 2009 | Frequency - non-health
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	111,781,000	111,741,000	105,493,000	103,833,000	99,832,000	94,851,000	81,055,000	62,220,000	26,518,000	0
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	31,000
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	111,812,000	111,741,000	112,312,000	107,323,000	106,040,000	109,936,000	101,259,000	91,523,000	79,796,000	0
Short-duration Insurance Contracts, Accident Year 2009 | Severity
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	4,463,000	4,194,000	4,172,000	3,952,000	3,902,000	3,753,000	3,364,000	2,582,000	276,000	0
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	6,381,000
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	10,844,000	10,796,000	10,820,000	14,010,000	14,183,000	14,329,000	14,970,000	15,372,000	19,093,000	0
Short-duration Insurance Contracts, Accident Year 2010 | Health
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	36,107,000	36,107,000	36,107,000	36,120,000	36,120,000	41,477,000	35,609,000	17,771,000	0	0
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	0
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	36,107,000	36,107,000	36,107,000	36,120,000	36,120,000	49,492,000	35,968,000	36,066,000	0	0
Short-duration Insurance Contracts, Accident Year 2010 | Frequency - non-health
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	176,201,000	176,146,000	161,725,000	156,396,000	143,989,000	127,823,000	100,334,000	50,177,000	0	0
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	392,000
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	176,594,000	176,608,000	173,764,000	165,504,000	161,414,000	162,112,000	144,489,000	130,449,000	0	0
Short-duration Insurance Contracts, Accident Year 2010 | Severity
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	11,788,000	11,588,000	6,069,000	5,899,000	1,237,000	1,112,000	862,000	281,000	0	0
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	2,570,000
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	14,358,000	14,507,000	14,194,000	14,291,000	14,042,000	14,079,000	5,147,000	4,522,000	0	0
Short-duration Insurance Contracts, Accident Year 2011 | Health
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	35,533,000	35,533,000	35,533,000	35,737,000	35,755,000	35,615,000	27,104,000	0	0	0
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	0
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	35,533,000	35,540,000	35,533,000	35,737,000	35,755,000	36,145,000	36,088,000	0	0	0
Short-duration Insurance Contracts, Accident Year 2011 | Frequency - non-health
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	253,421,000	252,684,000	203,255,000	185,591,000	168,209,000	134,140,000	78,846,000	0	0	0
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	1,563,000
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	254,984,000	254,723,000	235,787,000	212,697,000	200,216,000	189,690,000	173,216,000	0	0	0
Short-duration Insurance Contracts, Accident Year 2011 | Severity
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	5,054,000	5,048,000	5,047,000	5,044,000	5,038,000	5,033,000	24,000	0	0	0
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	28,000
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	5,082,000	5,081,000	5,074,000	5,079,000	5,068,000	5,069,000	5,071,000	0	0	0
Short-duration Insurance Contracts, Accident Year 2012 | Health
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	9,621,000	9,621,000	9,621,000	9,723,000	9,670,000	9,342,000	0	0	0	0
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	0
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	9,621,000	9,621,000	9,621,000	9,723,000	9,781,000	10,494,000	0	0	0	0
Short-duration Insurance Contracts, Accident Year 2012 | Frequency - non-health
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	285,290,000	283,653,000	262,086,000	253,949,000	236,556,000	121,538,000	0	0	0	0
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	2,192,000
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	287,482,000	286,548,000	287,025,000	270,409,000	271,334,000	268,511,000	0	0	0	0
Short-duration Insurance Contracts, Accident Year 2012 | Severity
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	0	0	0	0	0	0	0	0	0	0
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	0
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	0	0	0	0	0	15,000,000	0	0	0	0
Short-duration Insurance Contracts, Accident Year 2013 | Health
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	47,032,000	47,045,000	47,112,000	46,969,000	34,515,000	0	0	0	0	0
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	0
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	47,032,000	47,045,000	47,301,000	46,969,000	43,895,000	0	0	0	0	0
Short-duration Insurance Contracts, Accident Year 2013 | Frequency - non-health
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	305,782,000	301,772,000	291,231,000	264,730,000	145,593,000	0	0	0	0	0
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	3,912,000
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	309,694,000	308,783,000	306,524,000	305,919,000	309,833,000	0	0	0	0	0
Short-duration Insurance Contracts, Accident Year 2013 | Severity
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	1,502,000	1,491,000	1,224,000	729,000	94,000	0	0	0	0	0
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	0
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	1,502,000	1,501,000	1,507,000	1,807,000	2,885,000	0	0	0	0	0
Short-duration Insurance Contracts, Accident Year 2014 | Health
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	29,042,000	29,159,000	28,486,000	19,040,000	0	0	0	0	0	0
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	0
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	29,042,000	29,455,000	30,154,000	32,845,000	0	0	0	0	0	0
Short-duration Insurance Contracts, Accident Year 2014 | Frequency - non-health
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	172,834,000	161,064,000	149,445,000	82,244,000	0	0	0	0	0	0
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	11,151,000
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	183,986,000	181,753,000	178,247,000	178,117,000	0	0	0	0	0	0
Short-duration Insurance Contracts, Accident Year 2014 | Severity
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	2,974,000	2,933,000	2,457,000	1,558,000	0	0	0	0	0	0
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	1,772,000
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	4,745,000	4,624,000	4,750,000	4,749,000	0	0	0	0	0	0
Short-duration Insurance Contracts, Accident Year 2015 | Health
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	34,201,000	32,043,000	14,561,000	0	0	0	0	0	0	0
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	0
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	34,201,000	33,576,000	34,136,000	0	0	0	0	0	0	0
Short-duration Insurance Contracts, Accident Year 2015 | Frequency - non-health
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	199,029,000	179,725,000	109,376,000	0	0	0	0	0	0	0
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	37,080,000
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	236,109,000	230,745,000	225,244,000	0	0	0	0	0	0	0
Short-duration Insurance Contracts, Accident Year 2015 | Severity
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	4,408,000	1,306,000	473,000	0	0	0	0	0	0	0
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	5,753,000
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	10,161,000	8,354,000	8,204,000	0	0	0	0	0	0	0
Short-duration Insurance Contracts, Accident Year 2016 | Health
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	39,850,000	20,601,000	0	0	0	0	0	0	0	0
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	1,456,000
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	41,305,000	37,726,000	0	0	0	0	0	0	0	0
Short-duration Insurance Contracts, Accident Year 2016 | Frequency - non-health
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	222,207,000	132,142,000	0	0	0	0	0	0	0	0
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	82,755,000
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	304,962,000	291,180,000	0	0	0	0	0	0	0	0
Short-duration Insurance Contracts, Accident Year 2016 | Severity
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	4,103,000	876,000	0	0	0	0	0	0	0	0
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	16,005,000
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	20,108,000	17,265,000	0	0	0	0	0	0	0	0
Short-duration Insurance Contracts, Accident Year 2017 | Health
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	23,814,000	0	0	0	0	0	0	0	0	0
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	20,725,000
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	44,539,000	0	0	0	0	0	0	0	0	0
Short-duration Insurance Contracts, Accident Year 2017 | Frequency - non-health
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	181,431,000	0	0	0	0	0	0	0	0	0
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	185,910,000
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	367,342,000	0	0	0	0	0	0	0	0	0
Short-duration Insurance Contracts, Accident Year 2017 | Severity
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	15,053,000	0	0	0	0	0	0	0	0	0
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	43,606,000
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	$ 58,659,000	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0