INVESTMENTS - Equity Investments (Details) - USD ($)	3 Months Ended			9 Months Ended
	Sep. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Investment Holdings [Line Items]
Amortized Cost	$ 11,897,000			$ 11,897,000		$ 23,856,000
Gross Unrealized Gain	185,000			185,000		46,190,000
Gross Unrealized Loss	1,646,000			1,646,000		0
Fair Value	10,436,000			10,436,000		70,046,000
Realized gain on sale of equity investment	0		$ 0	(22,052,000)	$ 0
Common Stock | Common Class B
Investment Holdings [Line Items]
Amortized Cost	618,000			618,000		15,716,000
Gross Unrealized Gain	185,000			185,000		45,565,000
Gross Unrealized Loss	0			0		0
Fair Value	803,000			803,000		61,281,000
Realized gain on sale of equity investment				(22,100,000)
Unrealized gains on equity investments, net				200,000	25,600,000
Other investments
Investment Holdings [Line Items]
Amortized Cost	11,279,000			11,279,000		8,140,000
Gross Unrealized Gain	0			0		625,000
Gross Unrealized Loss	1,646,000			1,646,000		0
Fair Value	$ 9,633,000			9,633,000		$ 8,765,000
Impairment loss		$ 2,300,000			$ 0
Consideration				$ 2,400,000