INVESTMENTS (Gross Unrealized Losses) (Details) $ in Thousands	Jun. 30, 2019 USD ($) security	Dec. 31, 2018 USD ($) security
U.S. government and agency
Fixed maturities
Fair Value - 12 months or greater	$ 111,237	$ 374,030
Unrealized Losses - 12 months or greater	(1,085)	(7,659)
Fair Value - Less than 12 months	174,271	424,439
Unrealized Losses - Less than 12 months	(180)	(1,018)
Total Fair Value of Securities in Unrealized Loss Position	285,508	798,469
Total Unrealized Losses	(1,265)	(8,677)
Non-U.S. government
Fixed maturities
Fair Value - 12 months or greater	130,187	44,339
Unrealized Losses - 12 months or greater	(6,343)	(2,004)
Fair Value - Less than 12 months	111,035	303,376
Unrealized Losses - Less than 12 months	(2,380)	(14,116)
Total Fair Value of Securities in Unrealized Loss Position	241,222	347,715
Total Unrealized Losses	(8,723)	(16,120)
Corporate debt
Fixed maturities
Fair Value - 12 months or greater	479,376	1,439,378
Unrealized Losses - 12 months or greater	(10,405)	(58,915)
Fair Value - Less than 12 months	484,354	2,547,135
Unrealized Losses - Less than 12 months	(8,742)	(69,529)
Total Fair Value of Securities in Unrealized Loss Position	963,730	3,986,513
Total Unrealized Losses	(19,147)	(128,444)
Agency RMBS
Fixed maturities
Fair Value - 12 months or greater	557,096	940,645
Unrealized Losses - 12 months or greater	(6,256)	(29,255)
Fair Value - Less than 12 months	66,210	117,181
Unrealized Losses - Less than 12 months	(119)	(629)
Total Fair Value of Securities in Unrealized Loss Position	623,306	1,057,826
Total Unrealized Losses	(6,375)	(29,884)
CMBS
Fixed maturities
Fair Value - 12 months or greater	18,034	455,582
Unrealized Losses - 12 months or greater	(27)	(11,430)
Fair Value - Less than 12 months	136,832	353,802
Unrealized Losses - Less than 12 months	(688)	(2,365)
Total Fair Value of Securities in Unrealized Loss Position	154,866	809,384
Total Unrealized Losses	(715)	(13,795)
Non-Agency RMBS
Fixed maturities
Fair Value - 12 months or greater	5,845	9,494
Unrealized Losses - 12 months or greater	(973)	(1,170)
Fair Value - Less than 12 months	15,760	11,432
Unrealized Losses - Less than 12 months	(340)	(112)
Total Fair Value of Securities in Unrealized Loss Position	21,605	20,926
Total Unrealized Losses	(1,313)	(1,282)
ABS
Fixed maturities
Fair Value - 12 months or greater	400,246	237,237
Unrealized Losses - 12 months or greater	(3,609)	(2,755)
Fair Value - Less than 12 months	487,791	1,150,692
Unrealized Losses - Less than 12 months	(2,337)	(12,485)
Total Fair Value of Securities in Unrealized Loss Position	888,037	1,387,929
Total Unrealized Losses	(5,946)	(15,240)
Municipals
Fixed maturities
Fair Value - 12 months or greater	9,980	68,814
Unrealized Losses - 12 months or greater	(120)	(1,373)
Fair Value - Less than 12 months	0	9,894
Unrealized Losses - Less than 12 months	0	(24)
Total Fair Value of Securities in Unrealized Loss Position	9,980	78,708
Total Unrealized Losses	(120)	(1,397)
Fixed maturities
Fixed maturities
Fair Value - 12 months or greater	1,712,001	3,569,519
Unrealized Losses - 12 months or greater	(28,818)	(114,561)
Fair Value - Less than 12 months	1,476,253	4,917,951
Unrealized Losses - Less than 12 months	(14,786)	(100,278)
Total Fair Value of Securities in Unrealized Loss Position	3,188,254	8,487,470
Total Unrealized Losses	$ (43,604)	$ (214,839)
Number of available for sale securities in unrealized loss positions | security	1,614	3,599
Number of available for sale securities in unrealized loss positions for 12 months or greater | security	958	1,656
Fixed maturities | Below Investment Grade or Not Rated
Fixed maturities
Total Unrealized Losses	$ (12,000)	$ (49,000)