UNALLOCATED RESERVE AND DISTRIBUTIONS (Details) - USD ($)		3 Months Ended		9 Months Ended
	Oct. 13, 2017	Oct. 31, 2017	Oct. 31, 2016	Oct. 31, 2017	Oct. 31, 2016	Jan. 31, 2017
UNALLOCATED RESERVE AND DISTRIBUTIONS
Distribution declared or paid (in dollars per unit)	$ 0.64	$ 0.6400	$ 0.1000	$ 1.3500	$ 0.5000
Unallocated Cash and Securities portion of Unallocated Reserve
Cash and U.S. Government securities		$ 26,485,373		$ 26,485,373		$ 14,151,226
Distribution payable		(8,396,806)		(8,396,806)		(1,836,801)
Unallocated cash and U.S. Government securities		18,088,567		18,088,567		$ 12,314,425
Reconciliation of Trust's Unallocated Reserve
Unallocated Reserve at the beginning of the period				10,205,470
Net income		11,964,245	$ 3,208,151	28,440,087	$ 5,198,145
Distributions declared				(17,712,014)
Unallocated Reserve at the end of the period		$ 20,933,543		$ 20,933,543