INVESTMENTS (Net Investment Income) (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Net Investment Income [Line Items]
Gross investment income	$ 116,648	$ 112,894	$ 224,223	$ 218,752
Investment expenses	(6,688)	(6,831)	(13,262)	(14,024)
Net investment income	109,960	106,063	210,961	204,728
Fixed maturities
Net Investment Income [Line Items]
Gross investment income	88,320	78,218	172,279	155,625
Other investments
Net Investment Income [Line Items]
Gross investment income	14,541	23,639	28,246	42,601
Equity securities
Net Investment Income [Line Items]
Gross investment income	3,158	4,347	4,916	7,825
Mortgage loans
Net Investment Income [Line Items]
Gross investment income	3,357	2,597	6,483	5,074
Cash and cash equivalents
Net Investment Income [Line Items]
Gross investment income	5,627	3,433	9,779	6,529
Short-term investments
Net Investment Income [Line Items]
Gross investment income	$ 1,645	$ 660	$ 2,520	$ 1,098

The net gain or loss (both realized and unrealized) related to investments in certain entities that calculate net asset value per share and the amount after accretion (amortization) of discount (premium), of interest income and dividend income on nonoperating securities.

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The net gain or loss (both realized and unrealized) related to investments in certain entities that calculate net asset value per share and the amount after accretion (amortization) of discount (premium) of interest income and dividend income on nonoperating securities, net of investment expense.

+ References

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Amount of expenses related to the generation of investment income.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.9)
-URI http://asc.fasb.org/extlink&oid=115205541&loc=SL114868664-224227

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04.2)
-URI http://asc.fasb.org/extlink&oid=114873790&loc=SL114874131-224263

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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