INVESTMENTS - Equity Investments (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Investment Holdings [Line Items]
Amortized Cost	$ 11,776,000		$ 11,776,000		$ 23,856,000
Gross Unrealized Gain	81,000		81,000		46,190,000
Gross Unrealized Loss	1,646,000		1,646,000		0
Fair Value	10,211,000		10,211,000		70,046,000
Realized gain on sale of equity investment	(22,052,000)	$ 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	81,000		81,000		45,565,000
Gross Unrealized Loss	0		0		0
Fair Value	699,000		699,000		61,281,000
Realized gain on sale of equity investment	(22,100,000)
Unrealized (losses) gains on equity investments, net			100,000	4,200,000
Other investments
Investment Holdings [Line Items]
Amortized Cost	11,158,000		11,158,000		8,140,000
Gross Unrealized Gain	0		0		625,000
Gross Unrealized Loss	1,646,000		1,646,000		0
Fair Value	$ 9,512,000		9,512,000		$ 8,765,000
Impairment loss			$ 2,300,000	$ 0