INVESTMENTS (Details 2) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Schedule Of Available For Sale Securities [Line Items]
Due in one year or less (amortized cost)	$ 434,283	$ 313,287
Due after one year through five years (amortized cost)	3,834,452	3,906,190
Due after five years through ten years (amortized cost)	2,258,136	2,546,299
Due after ten years (amortized cost)	210,174	326,206
Total fixed maturities with a single maturity date (amortized cost)	6,737,045	7,091,982
Total (amortized cost)	11,043,394	11,523,316
Due in one year or less (fair value)	432,662	305,972
Due after one year through five years (fair value)	3,850,174	3,850,149
Due after five years through ten years (fair value)	2,276,190	2,510,975
Due after ten years (fair value)	218,115	319,511
Total fixed maturities with a single maturity date (fair value)	6,777,141	6,986,607
Fair Value (fixed maturities)	$ 11,086,386	$ 11,397,114
Due in one year or less (% of total fair value)	4.00%	2.80%
Due after one year through five years (% of total fair value)	34.70%	33.80%
Due after five years through ten years (% of total fair value)	20.50%	22.00%
Due after ten years (% of total fair value)	2.00%	2.80%
Fixed maturities with a single maturity date (% of total fair value)	61.20%	61.40%
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)	$ 2,313,096	$ 2,487,837
Total (amortized cost)	2,313,096	2,487,837
Fixed maturities without a single maturity date (fair value)	2,306,822	2,465,135
Fair Value (fixed maturities)	$ 2,306,822	$ 2,465,135
Fixed maturities without a single maturity date (% of total fair value)	20.80%	21.60%
CMBS [Member]
Schedule Of Available For Sale Securities [Line Items]
Fixed maturities without a single maturity date (amortized cost)	$ 665,520	$ 664,368
Total (amortized cost)	665,520	664,368
Fixed maturities without a single maturity date (fair value)	669,736	666,237
Fair Value (fixed maturities)	$ 669,736	$ 666,237
Fixed maturities without a single maturity date (% of total fair value)	6.00%	5.80%
Non-Agency RMBS [Member]
Schedule Of Available For Sale Securities [Line Items]
Fixed maturities without a single maturity date (amortized cost)	$ 42,653	$ 57,316
Total (amortized cost)	42,653	57,316
Fixed maturities without a single maturity date (fair value)	43,817	56,921
Fair Value (fixed maturities)	$ 43,817	$ 56,921
Fixed maturities without a single maturity date (% of total fair value)	0.40%	0.50%
ABS [Member]
Schedule Of Available For Sale Securities [Line Items]
Fixed maturities without a single maturity date (amortized cost)	$ 1,285,080	$ 1,221,813
Total (amortized cost)	1,285,080	1,221,813
Fixed maturities without a single maturity date (fair value)	1,288,870	1,222,214
Fair Value (fixed maturities)	$ 1,288,870	$ 1,222,214
Fixed maturities without a single maturity date (% of total fair value)	11.60%	10.70%