SUBSEQUENT EVENTS (Details)	12 Months Ended		161 Months Ended
	Dec. 31, 2020 USD ($) shares	Dec. 31, 2019 USD ($) shares	Dec. 31, 2020 USD ($) $ / item shares
Subsequent events
Number of depository receipts repurchased			1,428,437
Repurchase price of depository receipts (in dollars per receipt) | $ / item			28.43
Total cost of repurchase | $	$ 394,031	$ 4,050,137	$ 44,718,000
Units required to be repurchased (in shares)	222	2,408
Class B
Subsequent events
Number of depository receipts repurchased			3,572
Total cost of repurchase | $	$ 74,870	$ 769,458
Units required to be repurchased (in shares)	42.18	457.6
General Partnership
Subsequent events
Number of depository receipts repurchased			188
Total cost of repurchase | $	$ 3,941	$ 40,498
Units required to be repurchased (in shares)	2.22	24.1