FAIR VALUE OF FINANCIAL INSTRUMENTS - Reconciliation of Beginning and Ending Balances for Fair Value Measurements (Details) - USD ($)	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Transfers
Securities transferred into Level 3	$ 0	$ 44,100,000
Securities transferred into Level 2 from Level 3	9,300,000	106,100,000
Securities transferred from Level 2 to Level 1	0	12,200,000
Securities transferred out of Level 1	0	100,000
Level 3
Assets:
Beginning Balance	1,498,010,000	1,795,178,000
Total Realized and Unrealized Gains Included in Earnings	8,753,000	11,612,000
Total Realized and Unrealized Gains Included in Other Comprehensive Income	11,301,000	14,922,000
Total Realized and Unrealized Losses Included in Earnings	(17,452,000)	(22,310,000)
Total Realized and Unrealized Losses Included in Other Comprehensive Income	(1,113,000)	(19,344,000)
Purchases	37,259,000	17,429,000
Sales	(60,210,000)	(81,237,000)
Transfers in and/or out of Level 3	(9,287,000)	(62,029,000)
Other	319,000	(2,738,000)
Ending Balance	1,467,580,000	1,651,483,000
Total Gains (losses) included in Earnings related to Instruments still held at the Reporting Date	(8,698,000)	(13,258,000)
Liabilities:
Beginning Balance	493,419,000	468,360,000
Total Realized and Unrealized Gains Included in Earnings	15,280,000	368,000
Total Realized and Unrealized Losses Included in Earnings	(49,165,000)	(121,324,000)
Issuances	180,000	187,000
Settlements	2,268,000	3,142,000
Ending Balance	525,216,000	586,361,000
Total Gains (losses) included in Earnings related to Instruments still held at the Reporting Date	(32,998,000)	(120,390,000)
Level 3 | Annuity account
Liabilities:
Beginning Balance	87,616,000	92,512,000
Total Realized and Unrealized Losses Included in Earnings	(887,000)	(566,000)
Issuances	180,000	187,000
Settlements	2,268,000	3,142,000
Ending Balance	86,415,000	90,123,000
Level 3 | Other liabilities
Liabilities:
Beginning Balance	405,803,000	375,848,000
Total Realized and Unrealized Gains Included in Earnings	15,280,000	368,000
Total Realized and Unrealized Losses Included in Earnings	(48,278,000)	(120,758,000)
Ending Balance	438,801,000	496,238,000
Total Gains (losses) included in Earnings related to Instruments still held at the Reporting Date	(32,998,000)	(120,390,000)
Level 3 | Total investments
Assets:
Beginning Balance	1,498,010,000	1,795,178,000
Total Realized and Unrealized Gains Included in Earnings	8,753,000	11,612,000
Total Realized and Unrealized Gains Included in Other Comprehensive Income	11,301,000	14,922,000
Total Realized and Unrealized Losses Included in Earnings	(17,452,000)	(22,310,000)
Total Realized and Unrealized Losses Included in Other Comprehensive Income	(1,113,000)	(19,344,000)
Purchases	37,259,000	17,429,000
Sales	(60,210,000)	(81,237,000)
Transfers in and/or out of Level 3	(9,287,000)	(62,029,000)
Other	319,000	(2,738,000)
Ending Balance	1,467,580,000	1,651,483,000
Total Gains (losses) included in Earnings related to Instruments still held at the Reporting Date	(8,698,000)	(13,258,000)
Level 3 | Fixed maturities
Assets:
Beginning Balance	1,316,708,000	1,660,290,000
Total Realized and Unrealized Gains Included in Earnings	3,508,000	7,395,000
Total Realized and Unrealized Gains Included in Other Comprehensive Income	11,301,000	14,922,000
Total Realized and Unrealized Losses Included in Earnings	(586,000)	(5,328,000)
Total Realized and Unrealized Losses Included in Other Comprehensive Income	(1,113,000)	(19,344,000)
Purchases	37,259,000	16,000,000
Sales	(60,210,000)	(81,237,000)
Transfers in and/or out of Level 3	(9,290,000)	(62,029,000)
Other	320,000	(2,738,000)
Ending Balance	1,297,897,000	1,527,931,000
Total Gains (losses) included in Earnings related to Instruments still held at the Reporting Date	2,922,000	(493,000)
Level 3 | Fixed maturities | Available-for-sale securities
Assets:
Beginning Balance	1,226,653,000	1,489,153,000
Total Realized and Unrealized Gains Included in Earnings		6,859,000
Total Realized and Unrealized Gains Included in Other Comprehensive Income	11,301,000	14,922,000
Total Realized and Unrealized Losses Included in Earnings		(4,135,000)
Total Realized and Unrealized Losses Included in Other Comprehensive Income	(1,113,000)	(19,344,000)
Purchases	37,259,000	16,000,000
Sales	(40,902,000)	(75,562,000)
Transfers in and/or out of Level 3	(9,290,000)	(53,722,000)
Other	(267,000)	(2,600,000)
Ending Balance	1,223,641,000	1,371,571,000
Level 3 | Fixed maturities | Trading Securities
Assets:
Beginning Balance	90,055,000	171,137,000
Total Realized and Unrealized Gains Included in Earnings	3,508,000	536,000
Total Realized and Unrealized Losses Included in Earnings	(586,000)	(1,193,000)
Sales	(19,308,000)	(5,675,000)
Transfers in and/or out of Level 3		(8,307,000)
Other	587,000	(138,000)
Ending Balance	74,256,000	156,360,000
Total Gains (losses) included in Earnings related to Instruments still held at the Reporting Date	2,922,000	(493,000)
Level 3 | Residential mortgage-backed securities | Available-for-sale securities
Assets:
Beginning Balance	3,000	3,000
Sales	(3,000)
Ending Balance	0	3,000
Level 3 | Commercial mortgage-backed securities | Available-for-sale securities
Assets:
Beginning Balance	0	0
Ending Balance	0	0
Level 3 | Other asset-backed securities | Available-for-sale securities
Assets:
Beginning Balance	562,604,000	587,031,000
Total Realized and Unrealized Gains Included in Earnings		6,859,000
Total Realized and Unrealized Gains Included in Other Comprehensive Income	3,530,000
Total Realized and Unrealized Losses Included in Other Comprehensive Income	(831,000)	(13,057,000)
Sales	(2,015,000)	(50,820,000)
Transfers in and/or out of Level 3	(6,643,000)	7,457,000
Other	291,000	361,000
Ending Balance	556,936,000	537,831,000
Level 3 | Other asset-backed securities | Trading Securities
Assets:
Beginning Balance	84,563,000	152,912,000
Total Realized and Unrealized Gains Included in Earnings	3,474,000	228,000
Total Realized and Unrealized Losses Included in Earnings	(586,000)	(934,000)
Sales	(19,308,000)	(1,603,000)
Transfers in and/or out of Level 3		172,000
Other	609,000	(92,000)
Ending Balance	68,752,000	150,683,000
Total Gains (losses) included in Earnings related to Instruments still held at the Reporting Date	2,888,000	(709,000)
Level 3 | Corporate securities | Available-for-sale securities
Assets:
Beginning Balance	664,046,000	902,119,000
Total Realized and Unrealized Gains Included in Other Comprehensive Income	7,771,000	14,922,000
Total Realized and Unrealized Losses Included in Earnings		(4,135,000)
Total Realized and Unrealized Losses Included in Other Comprehensive Income	(282,000)	(6,287,000)
Purchases	37,259,000	16,000,000
Sales	(38,884,000)	(24,742,000)
Transfers in and/or out of Level 3	(2,647,000)	(61,179,000)
Other	(558,000)	(2,961,000)
Ending Balance	666,705,000	833,737,000
Level 3 | Corporate securities | Trading Securities
Assets:
Beginning Balance	5,492,000	18,225,000
Total Realized and Unrealized Gains Included in Earnings	34,000	308,000
Total Realized and Unrealized Losses Included in Earnings		(259,000)
Sales		(4,072,000)
Transfers in and/or out of Level 3		(8,479,000)
Other	(22,000)	(46,000)
Ending Balance	5,504,000	5,677,000
Total Gains (losses) included in Earnings related to Instruments still held at the Reporting Date	34,000	216,000
Level 3 | Equity securities
Assets:
Beginning Balance	65,786,000	66,504,000
Transfers in and/or out of Level 3	3,000
Other	(1,000)
Ending Balance	65,788,000	66,504,000
Total Gains (losses) included in Earnings related to Instruments still held at the Reporting Date	1,000
Level 3 | Other long-term investments
Assets:
Beginning Balance	115,516,000	68,384,000
Total Realized and Unrealized Gains Included in Earnings	5,245,000	4,217,000
Total Realized and Unrealized Losses Included in Earnings	(16,866,000)	(16,982,000)
Purchases		1,429,000
Ending Balance	103,895,000	57,048,000
Total Gains (losses) included in Earnings related to Instruments still held at the Reporting Date	$ (11,621,000)	$ (12,765,000)