FAIR VALUE MEASUREMENTS (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Investments in securities:
Investments in trading securities	$ 71,003	$ 51,324
Fair Value, Net Asset (Liability)	71,003	51,324
Inputs, Net Asset Value [Member]
Investments in securities:
Investments in trading securities	2,436	2,326
Level 1
Investments in securities:
Investments in trading securities	68,567	48,998
Fair Value, Net Asset (Liability)	68,567	48,998
Level 2
Investments in securities:
Investments in trading securities	0	0
Fair Value, Net Asset (Liability)	0	0
Level 3
Investments in securities:
Investments in trading securities	0	0
Fair Value, Net Asset (Liability)	$ 0	$ 0