ROYALTY AGREEMENT, UNALLOCATED RESERVE AND DISTRIBUTIONS (Details) - USD ($)		3 Months Ended		9 Months Ended
	Oct. 11, 2018	Oct. 31, 2018	Oct. 31, 2017	Oct. 31, 2018	Oct. 31, 2017	Jan. 31, 2018
UNALLOCATED RESERVE AND DISTRIBUTIONS
Distribution declared or paid (in dollars per unit)	$ 0.94	$ 0.9400	$ 0.6400	$ 1.6100	$ 1.3500
Unallocated Cash and Securities portion of Unallocated Reserve
Cash and U.S. Government securities		$ 33,176,860		$ 33,176,860		$ 24,112,286
Distribution payable		(12,332,809)		(12,332,809)		(15,481,612)
Unallocated cash and U.S. Government securities		20,844,051		20,844,051		$ 8,630,674
Reconciliation of Trust's Unallocated Reserve
Unallocated Reserve at the beginning of the period				10,606,675
Net income		13,585,062	$ 10,697,669	38,772,365	$ 29,166,548
Distributions declared				(21,123,216)
Unallocated Reserve at the end of the period		$ 28,255,824		$ 28,255,824