INVESTMENTS - (Net Realized Gains (Losses) by Major Investment Category (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Gross realized and unrealized gains:
Total gross realized and unrealized gains	$ 29,057	$ 8,757	$ 2,797
Total gross realized and unrealized losses	(11,025)	(1,673)	(6,941)
Net realized and unrealized gains (losses) on investments	18,032	7,084	(4,144)
Debt securities
Gross realized and unrealized gains:
Total gross realized and unrealized gains	20,470	2,829	423
Total gross realized and unrealized losses	(2,879)	(664)	(3,990)
Equity securities
Gross realized and unrealized gains:
Total gross realized and unrealized gains	8,587	5,928	2,374
Total gross realized and unrealized losses	$ (8,146)	$ (1,009)	$ (2,951)