CONSOLIDATED QUARTERLY RESULTS - UNAUDITED (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Gross premiums and policy fees	$ 1,052,516	$ 1,045,148	$ 1,009,112	$ 896,165	$ 1,172,267	$ 1,021,152	$ 939,097	$ 923,686	$ 4,002,941	$ 4,056,202	$ 3,656,508
Reinsurance ceded	(361,922)	(303,732)	(376,573)	(53,318)	(565,812)	(330,201)	(352,915)	(331,517)	(1,095,545)	(1,580,445)	(1,383,510)
Net premiums and policy fees	690,594	741,416	632,539	842,847	606,455	690,951	586,182	592,169	2,907,396	2,475,757	2,272,998
Net investment income	651,377	738,171	740,435	752,980	752,503	739,711	685,194	641,422	2,882,963	2,818,830	2,338,902
Realized gains (losses)	(51,274)	38,156	20,102	(38,111)	(39,222)	119,685	43,545	53,078
Other income	184,172	115,484	111,364	127,170	119,168	115,679	104,172	78,136	538,190	417,155	321,019
Revenues	1,474,869	1,633,227	1,504,440	1,684,886	1,438,904	1,666,026	1,419,093	1,364,805	6,297,422	5,888,828	4,759,016
Total benefits and expenses	1,431,271	1,560,615	1,298,599	1,593,413	1,357,747	1,426,185	1,233,370	1,188,078	5,883,898	5,205,380	4,511,428
Income before income tax	43,598	72,612	205,841	91,473	81,157	239,841	185,723	176,727	413,524	683,448	247,588
Income tax expense	68	12,850	40,736	17,508	15,109	49,417	31,309	34,629	71,162	130,464	53,661
Net income	$ 43,530	$ 59,762	$ 165,105	$ 73,965	$ 66,048	$ 190,424	$ 154,414	$ 142,098	$ 342,362	$ 552,984	$ 193,927