ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) - Reclassifications (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Reclassifications Out of Accumulated Other Comprehensive Income (Loss)
Benefits and settlement expenses, net of reinsurance ceded	$ (1,258,824)	$ (1,171,034)	$ (3,735,160)	$ (3,147,641)
Tax (expense) benefit	(12,850)	(49,417)	(71,094)	(115,355)
Net credit losses recognized in operations	(38,459)		(120,540)
Net income	59,762	190,424	298,832	486,936
Amount Reclassified from Accumulated Other Comprehensive Income (Loss) | Gains and losses on derivative instruments
Reclassifications Out of Accumulated Other Comprehensive Income (Loss)
Benefits and settlement expenses, net of reinsurance ceded	(401)	(746)	(3,072)	(1,360)
Tax (expense) benefit	84	157	645	285
Net income	(317)	(589)	(2,427)	(1,075)
Amount Reclassified from Accumulated Other Comprehensive Income (Loss) | Unrealized gains and losses on available-for-sale securities
Reclassifications Out of Accumulated Other Comprehensive Income (Loss)
Tax (expense) benefit	7,513	(1,022)	16,011	(1,517)
Realized gains (losses) - investments	2,681	15,686	44,298	21,885
Net credit losses recognized in operations	(38,459)		(120,540)
Net credit losses recognized in operations		(10,818)		(14,658)
Net income	$ (28,265)	$ 3,846	$ (60,231)	$ 5,710