OTHER COMPREHENSIVE INCOME (LOSS) (Tax Effects of Other Comprehensive Income) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Before Tax Amount
Other Comprehensive Income (Loss), before Tax	$ (84,871)	$ 87,860	$ (193,351)	$ 213,859
Tax (Expense) Benefit
Other Comprehensive Income (Loss), Tax	6,918	(4,253)	5,299	(7,712)
Net of Tax Amount
Other Comprehensive Income (Loss), Net of Tax	(77,953)	83,607	(188,052)	206,147
Unrealized gains (losses) on available for sale investments, net of tax:
Before Tax Amount
Unrealized investment gains (losses) arising during the period	(114,842)	80,557	(220,480)	150,929
Adjustment for reclassification of net realized investment (gains) losses and OTTI losses recognized in net income	39,100	(1,564)	34,987	24,194
Other Comprehensive Income (Loss), before Tax	(75,742)	78,993	(185,493)	175,123
Tax (Expense) Benefit
Unrealized investment gains (losses) arising during the period	9,562	(4,314)	3,046	(6,976)
Adjustment for reclassification of net realized investment (gains) losses and OTTI losses recognized in net income	(2,644)	61	2,253	(736)
Other Comprehensive Income (Loss), Tax	6,918	(4,253)	5,299	(7,712)
Net of Tax Amount
Unrealized investment gains (losses) arising during the period	(105,280)	76,243	(217,434)	143,953
Adjustment for reclassification of net realized investment (gains) losses and OTTI losses recognized in net income	36,456	(1,503)	37,240	23,458
Other Comprehensive Income (Loss), Net of Tax	(68,824)	74,740	(180,194)	167,411
Accumulated Other-than-Temporary Impairment, net of tax
Before Tax Amount
Other Comprehensive Income (Loss), before Tax	0	0	0	0
Tax (Expense) Benefit
Other Comprehensive Income (Loss), Tax	0	0	0	0
Net of Tax Amount
Other Comprehensive Income (Loss), Net of Tax	0	0	0	0
Cumulative foreign currency translation adjustments, net of tax:
Before Tax Amount
Other Comprehensive Income (Loss), before Tax	(9,129)	8,867	(7,858)	38,736
Tax (Expense) Benefit
Other Comprehensive Income (Loss), Tax	0	0	0	0
Net of Tax Amount
Other Comprehensive Income (Loss), Net of Tax	$ (9,129)	$ 8,867	$ (7,858)	$ 38,736