INVESTMENTS - Equity Securities (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2023	Dec. 31, 2022
Debt and Equity Securities, FV-NI [Line Items]
Cost	$ 561,558	$ 494,356
Gross unrealized gains	85,442	68,694
Gross unrealized losses	(90,738)	(77,797)
Fair value	556,262	485,253
Common stocks
Debt and Equity Securities, FV-NI [Line Items]
Cost	3,130	7,279
Gross unrealized gains	327	636
Gross unrealized losses	(407)	(442)
Fair value	3,050	7,473
Preferred stocks
Debt and Equity Securities, FV-NI [Line Items]
Cost	5,339	115
Gross unrealized gains	0	0
Gross unrealized losses	(253)	(43)
Fair value	5,086	72
Exchange-traded funds
Debt and Equity Securities, FV-NI [Line Items]
Cost	191,711	207,505
Gross unrealized gains	85,115	68,058
Gross unrealized losses	(3,032)	(5,757)
Fair value	273,794	269,806
Bond mutual funds
Debt and Equity Securities, FV-NI [Line Items]
Cost	361,378	279,457
Gross unrealized gains	0	0
Gross unrealized losses	(87,046)	(71,555)
Fair value	$ 274,332	$ 207,902