INVESTMENTS (Net Investment Income) (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Net Investment Income [Line Items]
Gross investment income	$ 144,734	$ 116,648	$ 258,099	$ 224,223
Investment expenses	(6,785)	(6,688)	(12,845)	(13,262)
Net investment income	137,949	109,960	245,254	210,961
Fixed maturities
Net Investment Income [Line Items]
Gross investment income	97,370	88,320	188,752	172,279
Other investments
Net Investment Income [Line Items]
Gross investment income	31,232	14,541	38,128	28,246
Equity securities
Net Investment Income [Line Items]
Gross investment income	3,197	3,158	5,525	4,916
Mortgage loans
Net Investment Income [Line Items]
Gross investment income	3,689	3,357	6,752	6,483
Cash and cash equivalents
Net Investment Income [Line Items]
Gross investment income	8,138	5,627	13,940	9,779
Short-term investments
Net Investment Income [Line Items]
Gross investment income	$ 1,108	$ 1,645	$ 5,002	$ 2,520

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=116634182&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=116637232&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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