UNALLOCATED RESERVE AND DISTRIBUTIONS (Details) - USD ($)		3 Months Ended		6 Months Ended
	Jul. 14, 2017	Jul. 31, 2017	Jul. 31, 2016	Jul. 31, 2017	Jul. 31, 2016	Jan. 31, 2017
UNALLOCATED RESERVE AND DISTRIBUTIONS
Distribution declared or paid (in dollars per unit)	$ 0.16	$ 0.1600	$ 0.2000	$ 0.7100	$ 0.4000
Unallocated Cash and Securities portion of Unallocated Reserve
Cash and U.S. Government securities		$ 13,163,944		$ 13,163,944		$ 14,151,226
Distribution payable		(2,099,202)		(2,099,202)		(1,836,801)
Unallocated cash and U.S. Government securities		11,064,742		11,064,742		$ 12,314,425
Reconciliation of Trust's Unallocated Reserve
Unallocated Reserve at the beginning of the period				10,205,470
Net income		13,114,135	$ 2,420,247	16,475,842	$ 1,989,995
Distributions declared				(9,315,208)
Unallocated Reserve at the end of the period		$ 17,366,104		$ 17,366,104