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INVESTMENTS - Realized and Unrealized Gains (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
INVESTMENTS
Net realized gains (losses), excluding OTTI									$ 63,624	$ 6,970	$ 34,740
OTTI									(217)	(2,559)	(95)
Total net realized gains (losses)	$ 15,507	$ 18,647	$ 20,849	$ 8,404	$ 5,111	$ 35	$ (1,359)	$ 624	63,407	4,411	34,645
Net changes in unrealized gains (losses) on investments:									(141,770)	54,323	(1,791)
Net unrealized losses on equity securities	$ (64,200)	$ 4,848	$ (12,611)	$ (26,772)					(98,735)
Net realized gains (losses) and changes in unrealized gains (losses) on investments									(78,363)	58,734	32,854
Goodwill and Intangible Asset Impairment									4,400
Debt securities \| Available for sale securities
INVESTMENTS
Net realized gains (losses), excluding OTTI									(2,018)	859	4,314
Net changes in unrealized gains (losses) on investments:									(41,778)	16,846	(10,972)
Equity securities
INVESTMENTS
Net realized gains (losses), excluding OTTI									69,868	10,282	38,709
Net unrealized losses on equity securities									(98,380)	36,844	8,659
Other
INVESTMENTS
Net realized gains (losses), excluding OTTI									(4,226)	(4,171)	(8,283)
Net changes in unrealized gains (losses) on investments:									(355)	29
Equity Method Investments [Member]
INVESTMENTS
Net changes in unrealized gains (losses) on investments:									$ (1,257)	$ 604	$ 522