INVESTMENTS - Net Realized Gain or Loss on Investments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Debt And Equity Securities [Line Items]
Debt securities, gross realized gain	$ 82
Equity securities and other investments, gross realized gain	2
Gross realized gains	84
Gross realized gains		$ 9,823
Debt securities, gross realized loss	(16)
Equity securities and other investments, gross realized losses	(1,355)
Gross realized losses	(1,371)
Gross realized losses		(1,101)
Net realized gain (loss)	$ (1,287)
Net realized gain (loss)		8,722
Debt securities
Debt And Equity Securities [Line Items]
Gross realized gains		77
Gross realized losses		(87)
Equity securities and other investments
Debt And Equity Securities [Line Items]
Gross realized gains		9,746
Gross realized losses		$ (1,014)