FAIR VALUE MEASUREMENTS (Details) - USD ($)	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Investments in securities:
Investments in trading securities	$ 37,272,000		$ 50,324,000
Total assets measured at fair value	40,515,000		54,562,000
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	3,975,000	$ 0
Unrealized gains (losses) on private investments	(995,000)	0
Ending balance	$ 2,980,000	$ 0
Fair Value Inputs [Abstract] (Deprecated 2018-01-31)
Unobservable input -book value multiple - minimum	1.05
Unobservable input -book value multiple - maximum	1.25
Unobservable input -book value multiple - weighted average	1.12
Level 1
Investments in securities:
Investments in trading securities	$ 37,272,000		50,324,000
Total assets measured at fair value	37,272,000		50,324,000
Level 2
Investments in securities:
Investments in trading securities	0		0
Total assets measured at fair value	0		0
Level 3
Investments in securities:
Investments in trading securities	0		0
Total assets measured at fair value	2,980,000		3,975,000
Investments Measured at NAV
Investments in securities:
Investments in trading securities	0		0
Total assets measured at fair value	263,000		263,000
Private investment fund
Investments in securities:
Private	263,000		263,000
Private investment fund | Level 1
Investments in securities:
Private	0		0
Private investment fund | Level 2
Investments in securities:
Private	0		0
Private investment fund | Level 3
Investments in securities:
Private	0		0
Private investment fund | Investments Measured at NAV
Investments in securities:
Private	263,000		263,000
Private equity
Investments in securities:
Private	2,980,000		3,975,000
Private equity | Level 1
Investments in securities:
Private	0		0
Private equity | Level 2
Investments in securities:
Private	0		0
Private equity | Level 3
Investments in securities:
Private	2,980,000		3,975,000
Private equity | Investments Measured at NAV
Investments in securities:
Private	$ 0		$ 0