TREASURY UNITS (Details)			3 Months Ended	12 Months Ended			137 Months Ended
	Jan. 01, 2019 USD ($) shares	Mar. 10, 2015 shares	Mar. 31, 2019 USD ($) $ / item shares	Dec. 31, 2018 $ / item shares	Dec. 31, 2017 USD ($) $ / item shares	Dec. 31, 2016 USD ($) shares	Dec. 31, 2018 USD ($) $ / item shares	Aug. 20, 2007 shares
Treasury units				55,839			55,839
Period for repurchase of depository receipts		5 years
Depository receipts authorized to be repurchased		2,000,000						300,000
Number of depository receipts repurchased					549		1,365,306
Repurchase price of depository receipts (in dollars per receipt) | $ / item							27.14
Units repurchased (in shares)					23	965
Total cost of repurchase | $					$ 42,548	$ 1,634,945	$ 40,274,000
Subsequent event
Number of depository receipts repurchased			41,900
Repurchase price of depository receipts (in dollars per receipt) | $ / item			54.11
Total cost of repurchase | $			$ 2,267,072
General Partnership
Treasury units				559			559
Fixed distribution percentage of unit holders				1.00%
Number of depository receipts repurchased							162
Total cost of repurchase | $					$ 426	$ 16,181
General Partnership | Subsequent event
Units repurchased (in shares)	17
Total cost of repurchase | $	$ 28,338
Treasury Units
Units repurchased (in shares)					23	965
Class A
Fixed distribution percentage of unit holders				80.00%
Repurchase price of units (in dollars per unit) | $ / item							814.20
Total cost of repurchase | $					$ 34,038	$ 1,311,328
Class B
Fixed distribution percentage of unit holders				19.00%
Number of depository receipts repurchased							3,072
Total cost of repurchase | $					$ 8,084	$ 307,436
Class B | Subsequent event
Units repurchased (in shares)	332
Total cost of repurchase | $	$ 538,421
Class A
Treasury units				44,671			44,671
Repurchase price of depository receipts (in dollars per receipt) | $ / item					62.00
Repurchase price of units (in dollars per unit) | $ / item				1,860.00	1,860.00
Class A | Limited Partner
Total cost of repurchase | $					$ 34,038
Class B
Treasury units				10,609			10,609
Fixed distribution percentage of unit holders				19.00%
Class B | Limited Partner
Total cost of repurchase | $					$ 8,084
Class B | General Partnership
Repurchase price of units (in dollars per unit) | $ / item							926.26
Treasury Units | General Partnership
Units repurchased (in shares)					0.2
Treasury Units | Class B | Limited Partner
Units repurchased (in shares)					4.3