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
Transfers into Level 3	$ 0	$ 44,100,000
Securities transferred from level 3 to level 2	9,300,000	106,200,000
Transfers from Level 2 to Level 1	0	12,200,000
Transfers from Level 1	0	100,000
Level 3
Assets:
Beginning Balance	1,510,043,000	1,826,883,000
Total Realized and Unrealized Gains Included in Earnings	14,569,000	7,395,000
Total Realized and Unrealized Gains Included in Other Comprehensive Income	11,303,000	14,922,000
Total Realized and Unrealized Losses Included in Earnings	(5,174,000)	(35,462,000)
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/out of Level 3	(9,287,000)	(62,065,000)
Other	319,000	(2,737,000)
Ending Balance	1,497,709,000	1,664,355,000
Total Gains (losses) included in Earnings related to Instruments still held at the Reporting Date	12,026,000	(30,627,000)
Liabilities:
Beginning Balance	659,459,000	678,068,000
Total Realized and Unrealized Gains Included in Earnings	44,263,000	368,000
Total Realized and Unrealized Losses Included in Earnings	(60,381,000)	(217,159,000)
Issuances	180,000	187,000
Settlements	2,268,000	3,142,000
Ending Balance	673,489,000	891,904,000
Total Gains (losses) included in Earnings related to Instruments still held at the Reporting Date	(15,231,000)	(216,225,000)
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	571,843,000	585,556,000
Total Realized and Unrealized Gains Included in Earnings	44,263,000	368,000
Total Realized and Unrealized Losses Included in Earnings	(59,494,000)	(216,593,000)
Ending Balance	587,074,000	801,781,000
Total Gains (losses) included in Earnings related to Instruments still held at the Reporting Date	(15,231,000)	(216,225,000)
Level 3 | Total investments
Assets:
Beginning Balance	1,510,043,000	1,826,883,000
Total Realized and Unrealized Gains Included in Earnings	14,569,000	7,395,000
Total Realized and Unrealized Gains Included in Other Comprehensive Income	11,303,000	14,922,000
Total Realized and Unrealized Losses Included in Earnings	(5,174,000)	(35,462,000)
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/out of Level 3	(9,287,000)	(62,065,000)
Other	319,000	(2,737,000)
Ending Balance	1,497,709,000	1,664,355,000
Total Gains (losses) included in Earnings related to Instruments still held at the Reporting Date	12,026,000	(30,627,000)
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/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 | Equity securities
Assets:
Beginning Balance	69,010,000	69,763,000
Total Realized and Unrealized Gains Included in Other Comprehensive Income	2,000
Total Realized and Unrealized Losses Included in Earnings	(2,630,000)
Transfers in/out of Level 3	3,000	(36,000)
Other	(1,000)	1,000
Ending Balance	66,384,000	69,728,000
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	124,325,000	96,830,000
Total Realized and Unrealized Gains Included in Earnings	11,061,000
Total Realized and Unrealized Losses Included in Earnings	(1,958,000)	(30,134,000)
Ending Balance	133,428,000	66,696,000
Total Gains (losses) included in Earnings related to Instruments still held at the Reporting Date	9,103,000	(30,134,000)
Level 3 | Available-for-sale securities | Fixed maturities
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/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 | Available-for-sale securities | Residential mortgage-backed securities
Assets:
Beginning Balance	3,000	3,000
Sales	(3,000)
Ending Balance	0	3,000
Level 3 | Available-for-sale securities | Commercial mortgage-backed securities
Assets:
Beginning Balance	0	0
Ending Balance	0	0
Level 3 | Available-for-sale securities | Other asset-backed 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/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 | Available-for-sale securities | Corporate securities
Assets:
Beginning Balance	664,046,000	902,119,000
Total Realized and Unrealized Gains Included in Earnings		0
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/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 | Trading securities | Fixed maturities
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/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 | Trading securities | Other asset-backed 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/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 | Trading securities | Corporate 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/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