INVESTMENTS (Gross Unrealized Losses) (Details) $ in Thousands	Mar. 31, 2019 USD ($) security	Dec. 31, 2018 USD ($) security
U.S. government and agency
Fixed maturities
Fair Value - 12 months or greater	$ 371,995	$ 374,030
Unrealized Losses - 12 months or greater	(4,194)	(7,659)
Fair Value - Less than 12 months	220,718	424,439
Unrealized Losses - Less than 12 months	(318)	(1,018)
Total Fair Value of Securities in Unrealized Loss Position	592,713	798,469
Total Unrealized Losses	(4,512)	(8,677)
Non-U.S. government
Fixed maturities
Fair Value - 12 months or greater	95,715	44,339
Unrealized Losses - 12 months or greater	(3,368)	(2,004)
Fair Value - Less than 12 months	136,310	303,376
Unrealized Losses - Less than 12 months	(3,473)	(14,116)
Total Fair Value of Securities in Unrealized Loss Position	232,025	347,715
Total Unrealized Losses	(6,841)	(16,120)
Corporate debt
Fixed maturities
Fair Value - 12 months or greater	1,134,227	1,439,378
Unrealized Losses - 12 months or greater	(20,122)	(58,915)
Fair Value - Less than 12 months	727,267	2,547,135
Unrealized Losses - Less than 12 months	(13,602)	(69,529)
Total Fair Value of Securities in Unrealized Loss Position	1,861,494	3,986,513
Total Unrealized Losses	(33,724)	(128,444)
Agency RMBS
Fixed maturities
Fair Value - 12 months or greater	849,681	940,645
Unrealized Losses - 12 months or greater	(16,949)	(29,255)
Fair Value - Less than 12 months	26,971	117,181
Unrealized Losses - Less than 12 months	(129)	(629)
Total Fair Value of Securities in Unrealized Loss Position	876,652	1,057,826
Total Unrealized Losses	(17,078)	(29,884)
CMBS
Fixed maturities
Fair Value - 12 months or greater	244,188	455,582
Unrealized Losses - 12 months or greater	(1,500)	(11,430)
Fair Value - Less than 12 months	85,473	353,802
Unrealized Losses - Less than 12 months	(325)	(2,365)
Total Fair Value of Securities in Unrealized Loss Position	329,661	809,384
Total Unrealized Losses	(1,825)	(13,795)
Non-Agency RMBS
Fixed maturities
Fair Value - 12 months or greater	9,360	9,494
Unrealized Losses - 12 months or greater	(905)	(1,170)
Fair Value - Less than 12 months	12,111	11,432
Unrealized Losses - Less than 12 months	(116)	(112)
Total Fair Value of Securities in Unrealized Loss Position	21,471	20,926
Total Unrealized Losses	(1,021)	(1,282)
ABS
Fixed maturities
Fair Value - 12 months or greater	273,759	237,237
Unrealized Losses - 12 months or greater	(2,757)	(2,755)
Fair Value - Less than 12 months	846,715	1,150,692
Unrealized Losses - Less than 12 months	(6,591)	(12,485)
Total Fair Value of Securities in Unrealized Loss Position	1,120,474	1,387,929
Total Unrealized Losses	(9,348)	(15,240)
Municipals
Fixed maturities
Fair Value - 12 months or greater	42,745	68,814
Unrealized Losses - 12 months or greater	(452)	(1,373)
Fair Value - Less than 12 months	15,779	9,894
Unrealized Losses - Less than 12 months	(30)	(24)
Total Fair Value of Securities in Unrealized Loss Position	58,524	78,708
Total Unrealized Losses	(482)	(1,397)
Fixed maturities
Fixed maturities
Fair Value - 12 months or greater	3,021,670	3,569,519
Unrealized Losses - 12 months or greater	(50,247)	(114,561)
Fair Value - Less than 12 months	2,071,344	4,917,951
Unrealized Losses - Less than 12 months	(24,584)	(100,278)
Total Fair Value of Securities in Unrealized Loss Position	5,093,014	8,487,470
Total Unrealized Losses	$ (74,831)	$ (214,839)
Number of available for sale securities in unrealized loss positions \| security	2,521	3,599
Number of available for sale securities in unrealized loss positions for 12 months or greater \| security	1,553	1,656
Fixed maturities \| Below Investment Grade or Not Rated
Fixed maturities
Total Unrealized Losses	$ (15,000)	$ (49,000)

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for more than 12 months.

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