ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) - Reclassifications Out of Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Reclassifications out of accumulated other comprehensive income (loss)
Benefits and settlement expenses, net of reinsurance ceded	$ (749,642)	$ (714,545)
Income before income tax	112,349	171,842
Tax benefit (expense)	(36,935)	(56,494)
Net income	75,414	115,348
Realized investment gains (losses): All other investments	22,841	81,728
Net impairment losses recognized in earnings	(7,831)	(2,617)
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	(205)
Income before income tax	(205)
Tax benefit (expense)	72
Net income	(133)
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)
Income before income tax	1,650	2,938
Tax benefit (expense)	(578)	(1,028)
Net income	1,072	1,910
Realized investment gains (losses): All other investments	9,481	5,555
Net impairment losses recognized in earnings	$ (7,831)	$ (2,617)