OTHER COMPREHENSIVE INCOME (LOSS) (Tax Effects of Other Comprehensive Income) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Before tax amount
Total other comprehensive income (loss), net of tax	$ 141,322	$ (84,871)	$ 364,664	$ (193,351)
Tax (expense) benefit
Total other comprehensive income (loss), net of tax	(14,273)	6,918	(31,409)	5,299
Net of tax amount
Total other comprehensive income (loss), net of tax	127,049	(77,953)	333,255	(188,052)
Available for sale investments
Before tax amount
Unrealized investment gains (losses) arising during the period	146,907	(114,842)	353,712	(220,480)
Adjustment for reclassification of net realized investment (gains) losses and OTTI losses recognized in net income	(8,141)	39,100	5,733	34,987
Total other comprehensive income (loss), net of tax	138,766	(75,742)	359,445	(185,493)
Tax (expense) benefit
Unrealized investment gains (losses) arising during the period	(15,465)	9,562	(32,061)	3,046
Adjustment for reclassification of net realized investment (gains) losses and OTTI losses recognized in net income	1,192	(2,644)	652	2,253
Total other comprehensive income (loss), net of tax	(14,273)	6,918	(31,409)	5,299
Net of tax amount
Unrealized investment gains (losses) arising during the period	131,442	(105,280)	321,651	(217,434)
Adjustment for reclassification of net realized investment (gains) losses and OTTI losses recognized in net income	(6,949)	36,456	6,385	37,240
Total other comprehensive income (loss), net of tax	124,493	(68,824)	328,036	(180,194)
Non-credit portion of OTTI losses
Before tax amount
Total other comprehensive income (loss), net of tax	0	0	0	0
Tax (expense) benefit
Total other comprehensive income (loss), net of tax	0	0	0	0
Net of tax amount
Total other comprehensive income (loss), net of tax	0	0	0	0
Foreign currency translation adjustment
Before tax amount
Total other comprehensive income (loss), net of tax	2,556	(9,129)	5,219	(7,858)
Tax (expense) benefit
Total other comprehensive income (loss), net of tax	0	0	0	0
Net of tax amount
Total other comprehensive income (loss), net of tax	$ 2,556	$ (9,129)	$ 5,219	$ (7,858)