INVESTMENTS (Details 3) $ in Thousands	Sep. 30, 2017 USD ($) security	Dec. 31, 2016 USD ($) security
Fixed Maturities [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair Value - 12 months or greater	$ 1,048,555	$ 971,489
Unrealized Losses - 12 months or greater	(35,602)	(77,645)
Fair Value - Less than 12 months	4,075,646	5,833,715
Unrealized Losses - Less than 12 months	(29,417)	(119,550)
Total Fair Value of Securities in Unrealized Loss Position	5,124,201	6,805,204
Total Unrealized Losses	$ (65,019)	$ (197,195)
Number of Available For Sale Securities In Unrealized Loss Positions | security	1,625	1,881
Number of Available For Sale Securities in Unrealized Loss Positions for 12 Months or Greater | security	403	330
Fixed Maturities [Member] | Below Investment Grade or Not Rated [Member]
Schedule Of Available For Sale Securities [Line Items]
Total Unrealized Losses	$ (6,000)	$ (15,000)
US Government and Agency [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair Value - 12 months or greater	161,425	54,051
Unrealized Losses - 12 months or greater	(5,641)	(2,729)
Fair Value - Less than 12 months	1,207,943	1,340,719
Unrealized Losses - Less than 12 months	(6,733)	(24,275)
Total Fair Value of Securities in Unrealized Loss Position	1,369,368	1,394,770
Total Unrealized Losses	(12,374)	(27,004)
Non-US Government [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair Value - 12 months or greater	61,872	149,360
Unrealized Losses - 12 months or greater	(7,354)	(38,683)
Fair Value - Less than 12 months	163,477	283,796
Unrealized Losses - Less than 12 months	(1,190)	(10,971)
Total Fair Value of Securities in Unrealized Loss Position	225,349	433,156
Total Unrealized Losses	(8,544)	(49,654)
Corporate Debt [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair Value - 12 months or greater	412,832	230,218
Unrealized Losses - 12 months or greater	(12,553)	(30,652)
Fair Value - Less than 12 months	990,308	1,948,976
Unrealized Losses - Less than 12 months	(9,047)	(44,488)
Total Fair Value of Securities in Unrealized Loss Position	1,403,140	2,179,194
Total Unrealized Losses	(21,600)	(75,140)
Agency RMBS [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair Value - 12 months or greater	350,010	76,694
Unrealized Losses - 12 months or greater	(8,130)	(1,101)
Fair Value - Less than 12 months	1,126,956	1,724,170
Unrealized Losses - Less than 12 months	(10,362)	(34,876)
Total Fair Value of Securities in Unrealized Loss Position	1,476,966	1,800,864
Total Unrealized Losses	(18,492)	(35,977)
CMBS [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair Value - 12 months or greater	13,919	84,640
Unrealized Losses - 12 months or greater	(238)	(749)
Fair Value - Less than 12 months	221,941	193,499
Unrealized Losses - Less than 12 months	(1,500)	(2,815)
Total Fair Value of Securities in Unrealized Loss Position	235,860	278,139
Total Unrealized Losses	(1,738)	(3,564)
Non-Agency RMBS [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair Value - 12 months or greater	8,342	13,642
Unrealized Losses - 12 months or greater	(803)	(1,752)
Fair Value - Less than 12 months	222	7,194
Unrealized Losses - Less than 12 months	(1)	(271)
Total Fair Value of Securities in Unrealized Loss Position	8,564	20,836
Total Unrealized Losses	(804)	(2,023)
ABS [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair Value - 12 months or greater	16,816	362,110
Unrealized Losses - 12 months or greater	(409)	(1,950)
Fair Value - Less than 12 months	323,886	266,763
Unrealized Losses - Less than 12 months	(373)	(893)
Total Fair Value of Securities in Unrealized Loss Position	340,702	628,873
Total Unrealized Losses	(782)	(2,843)
Municipals [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair Value - 12 months or greater	23,339	774
Unrealized Losses - 12 months or greater	(474)	(29)
Fair Value - Less than 12 months	40,913	68,598
Unrealized Losses - Less than 12 months	(211)	(961)
Total Fair Value of Securities in Unrealized Loss Position	64,252	69,372
Total Unrealized Losses	(685)	(990)
Equity Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair Value - 12 months or greater	33	4,959
Unrealized Losses - 12 months or greater	(135)	(461)
Fair Value - Less than 12 months	27,084	211,751
Unrealized Losses - Less than 12 months	(2,107)	(11,607)
Total Fair Value of Securities in Unrealized Loss Position	27,117	216,710
Total Unrealized Losses	$ (2,242)	$ (12,068)
Number of Available For Sale Securities In Unrealized Loss Positions | security	31	23
Number of Available For Sale Securities in Unrealized Loss Positions for 12 Months or Greater | security	2	3
Common Stock [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair Value - 12 months or greater	$ 33	$ 0
Unrealized Losses - 12 months or greater	(135)	0
Fair Value - Less than 12 months	2,939	37
Unrealized Losses - Less than 12 months	(434)	(342)
Total Fair Value of Securities in Unrealized Loss Position	2,972	37
Total Unrealized Losses	(569)	(342)
Exchange-Traded Funds [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair Value - 12 months or greater	0	4,959
Unrealized Losses - 12 months or greater	0	(461)
Fair Value - Less than 12 months	0	87,760
Unrealized Losses - Less than 12 months	0	(2,173)
Total Fair Value of Securities in Unrealized Loss Position	0	92,719
Total Unrealized Losses	0	(2,634)
Bond Mutual Funds [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair Value - 12 months or greater	0	0
Unrealized Losses - 12 months or greater	0	0
Fair Value - Less than 12 months	24,145	123,954
Unrealized Losses - Less than 12 months	(1,673)	(9,092)
Total Fair Value of Securities in Unrealized Loss Position	24,145	123,954
Total Unrealized Losses	$ (1,673)	$ (9,092)