INVESTMENTS - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Debt and Equity Securities, FV-NI [Line Items]
Equity securities and other investments, gross realized losses	$ 1,355,000
Mindjet
Debt and Equity Securities, FV-NI [Line Items]
Equity securities and other investments, gross realized losses	1,312,000
Voting interest percentage		19.30%
Carrying value of other investments	0	$ 2,300,000
Notes and interest receivable written off	$ 1,000,000