INVESTMENTS - Equity Investments (Details) - USD ($)	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Investment Holdings [Line Items]
Amortized Cost	$ 23,856,000		$ 23,856,000
Gross Unrealized Gain	48,504,000		46,190,000
Gross Unrealized Loss	1,646,000		0
Fair Value	70,714,000		70,046,000
Unrealized gains on equity investments, net	668,000	$ 3,798,000
Common Stock | Common Class B
Investment Holdings [Line Items]
Amortized Cost	15,716,000		15,716,000
Gross Unrealized Gain	48,504,000		45,565,000
Gross Unrealized Loss	0		0
Fair Value	64,220,000		61,281,000
Unrealized gains on equity investments, net	3,000,000.0	3,800,000
Other investments
Investment Holdings [Line Items]
Amortized Cost	8,140,000		8,140,000
Gross Unrealized Gain	0		625,000
Gross Unrealized Loss	1,646,000		0
Fair Value	6,494,000		$ 8,765,000
Impairment loss	$ 2,300,000	$ 0