INVESTMENTS (DETAILS 2) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Schedule Of Available For Sale Securities [Line Items]
Due in one year or less (amortized cost)	$ 313,287	$ 291,368
Due after one year through five years (amortized cost)	3,906,190	4,217,515
Due after five years through ten years (amortized cost)	2,546,299	2,263,684
Due after ten years (amortized cost)	326,206	312,431
Total fixed maturities with a single maturity date (amortized cost)	7,091,982	7,084,998
Total (amortized cost)	11,523,316	11,897,639
Due in one year or less (fair value)	305,972	289,571
Due after one year through five years (fair value)	3,850,149	4,142,802
Due after five years through ten years (fair value)	2,510,975	2,181,525
Due after ten years (fair value)	319,511	301,039
Total fixed maturities with a single maturity date (fair value)	6,986,607	6,914,937
Fair Value (fixed maturities)	$ 11,397,114	$ 11,719,749
Due in one year or less (% of total fair value)	2.80%	2.50%
Due after one year through five years (% of total fair value)	33.80%	35.30%
Due after five years through ten years (% of total fair value)	22.00%	18.60%
Due after ten years (% of total fair value)	2.80%	2.60%
Fixed maturities with a single maturity date (% of total fair value)	61.40%	59.00%
Total	100.00%	100.00%
Agency RMBS [Member]
Schedule Of Available For Sale Securities [Line Items]
Fixed maturities without a single maturity date (amortized cost)	$ 2,487,837	$ 2,236,138
Total (amortized cost)	2,487,837	2,236,138
Fixed maturities without a single maturity date (fair value)	2,465,135	2,249,236
Fair Value (fixed maturities)	$ 2,465,135	$ 2,249,236
Fixed maturities without a single maturity date (% of total fair value)	21.60%	19.20%
CMBS [Member]
Schedule Of Available For Sale Securities [Line Items]
Fixed maturities without a single maturity date (amortized cost)	$ 664,368	$ 1,088,595
Total (amortized cost)	664,368	1,088,595
Fixed maturities without a single maturity date (fair value)	666,237	1,083,298
Fair Value (fixed maturities)	$ 666,237	$ 1,083,298
Fixed maturities without a single maturity date (% of total fair value)	5.80%	9.20%
Non-Agency RMBS [Member]
Schedule Of Available For Sale Securities [Line Items]
Fixed maturities without a single maturity date (amortized cost)	$ 57,316	$ 99,989
Total (amortized cost)	57,316	99,989
Fixed maturities without a single maturity date (fair value)	56,921	101,008
Fair Value (fixed maturities)	$ 56,921	$ 101,008
Fixed maturities without a single maturity date (% of total fair value)	0.50%	0.90%
ABS [Member]
Schedule Of Available For Sale Securities [Line Items]
Fixed maturities without a single maturity date (amortized cost)	$ 1,221,813	$ 1,387,919
Total (amortized cost)	1,221,813	1,387,919
Fixed maturities without a single maturity date (fair value)	1,222,214	1,371,270
Fair Value (fixed maturities)	$ 1,222,214	$ 1,371,270
Fixed maturities without a single maturity date (% of total fair value)	10.70%	11.70%