INVESTMENTS (Equity Securities) (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
Sep. 30, 2019	Dec. 31, 2018
Debt and Equity Securities, FV-NI [Line Items]
Cost	$ 380,645	$ 365,905
Gross unrealized gains	61,876	33,610
Gross unrealized losses	(12,618)	(17,882)
Fair value	429,903	381,633
Common stocks
Debt and Equity Securities, FV-NI [Line Items]
Cost	504	790
Gross unrealized gains	67	112
Gross unrealized losses	(387)	(375)
Fair value	184	527
Exchange-traded funds
Debt and Equity Securities, FV-NI [Line Items]
Cost	215,620	213,420
Gross unrealized gains	61,809	33,498
Gross unrealized losses	(3,707)	(10,079)
Fair value	273,722	236,839
Bond mutual funds
Debt and Equity Securities, FV-NI [Line Items]
Cost	164,521	151,695
Gross unrealized gains	0	0
Gross unrealized losses	(8,524)	(7,428)
Fair value	$ 155,997	$ 144,267

Amount of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 45
-Paragraph 1A
-URI http://asc.fasb.org/extlink&oid=99377092&loc=SL75136599-209740

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Cost of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI). Excludes equity method investment and investment in equity security without readily determinable fair value.

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Amount of unrealized gain on investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 321
-SubTopic 10
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=116654751&loc=SL75117546-209714

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Amount of unrealized loss on investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

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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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