CONSOLIDATED QUARTERLY RESULTS - UNAUDITED (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Premiums and policy fees	$ 1,172,267	$ 1,021,152	$ 939,097	$ 923,686	$ 965,275	$ 871,892	$ 935,928	$ 883,413	$ 4,056,202	$ 3,656,508	$ 3,456,362
Reinsurance ceded	(549,922)	(314,234)	(337,077)	(315,971)	(378,112)	(267,910)	(391,864)	(345,624)	(1,517,204)	(1,383,510)	(1,367,096)
Net of reinsurance ceded	622,345	706,918	602,020	607,715	587,163	603,982	544,064	537,789	2,538,998	2,272,998	2,089,266
Net investment income	752,503	739,711	685,194	641,422	639,115	631,955	578,414	489,418	2,818,830	2,338,902	1,923,056
Realized investment gains (losses)	(19,427)	130,503	44,243	56,220	(24,005)	(46,866)	(32,583)	(40,725)
Net impairment losses recognized in earnings	(19,795)	(10,818)	(698)	(3,142)	(26,060)	(14)	(5)	(3,645)	(34,453)	(29,724)	(9,112)
Other income	119,168	115,679	104,172	78,136	79,685	80,906	79,754	80,674	417,155	321,019	325,411
Revenues	1,454,794	1,681,993	1,434,931	1,380,351	1,255,898	1,269,963	1,169,644	1,063,511	5,952,069	4,759,016	4,312,667
Total benefits and expenses	1,373,637	1,442,152	1,249,208	1,203,624	1,186,310	1,174,793	1,108,750	1,041,575	5,268,621	4,511,428	3,848,659
Income before income tax	81,157	239,841	185,723	176,727	69,588	95,170	60,894	21,936	683,448	247,588	464,008
Income tax expense	15,109	49,417	31,309	34,629	24,728	16,646	8,626	3,661	130,464	53,661	(718,409)
Net income	$ 66,048	$ 190,424	$ 154,414	$ 142,098	$ 44,860	$ 78,524	$ 52,268	$ 18,275	$ 552,984	$ 193,927	$ 1,182,417