QUARTERLY FINANCIAL DATA (UNAUDITED) (Details)	3 Months Ended								12 Months Ended
	Dec. 31, 2018 USD ($) $ / shares $ / item	Sep. 30, 2018 USD ($) $ / shares $ / item	Jun. 30, 2018 USD ($) $ / shares $ / item	Mar. 31, 2018 USD ($) $ / shares $ / item	Dec. 31, 2017 USD ($) $ / shares $ / item	Sep. 30, 2017 USD ($) $ / shares $ / item	Jun. 30, 2017 USD ($) $ / shares $ / item	Mar. 31, 2017 USD ($) $ / shares $ / item	Dec. 31, 2018 USD ($) $ / shares $ / item	Dec. 31, 2017 USD ($) $ / shares $ / item	Dec. 31, 2016 USD ($) $ / shares
QUARTERLY FINANCIAL DATA (UNAUDITED)
Revenue	$ 14,779,274	$ 14,545,533	$ 14,630,257	$ 14,059,000	$ 13,874,185	$ 13,421,805	$ 12,787,791	$ 12,743,607	$ 58,014,064	$ 52,827,388	$ 49,555,090
Expenses	10,710,144	11,329,228	10,759,024	10,297,296	10,369,714	10,493,852	8,817,160	9,001,696	43,095,692	38,682,422
Income Before Other Income (Expense)	4,069,130	3,216,305	3,871,233	3,761,704	3,504,471	2,927,953	3,970,631	3,741,911	14,918,372	14,144,966	13,259,950
Other Expenses	(2,492,253)	(2,555,976)	(3,817,907)	(1,883,146)	(1,816,201)	(2,056,233)	(1,486,924)	(1,847,677)	(10,749,282)	(7,207,035)	(8,309,098)
Net Income	$ 1,576,877	$ 660,329	$ 53,326	$ 1,878,558	$ 1,688,270	$ 871,720	$ 2,483,707	$ 1,894,234	$ 4,169,090	$ 6,937,931	$ 4,950,852
Net Income per Unit before Discontinued Operations | $ / shares	$ 12.68	$ 5.31	$ 0.43	$ 15.10	$ 13.56	$ 7.01	$ 19.97	$ 15.23	$ 33.52	$ 55.77
Net Income per Unit (in dollars per unit) | $ / shares	$ 12.68	$ 5.31	$ 0.43	$ 15.10	$ 13.56	$ 7.01	$ 19.97	$ 15.23	$ 33.52	$ 55.77	$ 39.62
Income Per Depositary Receipt Before Discontinued Operations (in dollars per unit) | $ / item	0.43	0.18	0.01	0.50	0.45	0.23	0.67	0.51	1.12	1.86
Net Income Per Depositary Receipt (in dollars per receipt) | $ / item	0.43	0.18	0.01	0.50	0.45	0.23	0.67	0.51	1.12	1.86