SUBSEQUENT EVENTS (Details)		1 Months Ended		3 Months Ended		6 Months Ended	132 Months Ended	142 Months Ended
	Aug. 31, 2007 shares	Aug. 05, 2019 USD ($) $ / item shares	Sep. 30, 2007 shares	Mar. 31, 2019 shares	Dec. 31, 2007 shares	Jun. 30, 2019 USD ($) shares	Dec. 31, 2018 shares	Jun. 30, 2019 USD ($) $ / item
Subsequent events
Number of depository receipts repurchased	1,413,200		1,413,200		1,413,200	1,413,200	1,413,200
Repurchase price of depository receipts (in dollars per receipt) | $ / item								28.09
Total cost of repurchase | $						$ 3,305,651		$ 43,579,000
Units required to be repurchased (in shares)						1,995
Subsequent event
Subsequent events
Number of depository receipts repurchased		1,660
Repurchase price of depository receipts (in dollars per receipt) | $ / item		60.20
Price per unit of depository receipts | $ / item		1,806.00
Total cost of repurchase | $		$ 99,972
Class B
Subsequent events
Number of depository receipts repurchased	345		345	345			345
Total cost of repurchase | $						$ 628,044
Class B | Subsequent event
Subsequent events
Units required to be repurchased (in shares)		13
Value of units required to be repurchased | $		$ 23,735
General Partnership
Subsequent events
Number of depository receipts repurchased	182		182	182			182
Total cost of repurchase | $						$ 33,055
Units required to be repurchased (in shares)						20
Value of units required to be repurchased | $						$ 33,055
General Partnership | Subsequent event
Subsequent events
Units required to be repurchased (in shares)		1
Value of units required to be repurchased | $		$ 1,249