OTHER COMPREHENSIVE INCOME (LOSS) (Reclassifications Out of AOCI Into Net Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Reclassification out of accumulated comprehensive income into net income available to common shareholders [Line Items]
Other realized investment gains (losses)	$ 22,059	$ (43,419)	$ 38,866	$ (57,835)
OTTI losses	(834)	(1,674)	(4,870)	(2,088)
Total before tax	188,877	101,132	296,678	173,301
Income tax (expense) benefit	(14,469)	(996)	(15,703)	40
Net income available to common shareholders	166,387	92,858	264,515	155,406
Unrealized investment gains (losses) on available for sale investments | Reclassification out of Accumulated Other Comprehensive Income
Reclassification out of accumulated comprehensive income into net income available to common shareholders [Line Items]
Other realized investment gains (losses)	8,975	(37,426)	(863)	(32,899)
OTTI losses	(834)	(1,674)	(4,870)	(2,088)
Total before tax	8,141	(39,100)	(5,733)	(34,987)
Income tax (expense) benefit	(1,192)	2,644	(652)	(2,253)
Net income available to common shareholders	$ 6,949	$ (36,456)	$ (6,385)	$ (37,240)