ROYALTY AGREEMENT, UNALLOCATED RESERVE AND DISTRIBUTIONS (Details) - USD ($)		3 Months Ended		6 Months Ended
	Jul. 12, 2019	Jul. 31, 2019	Jul. 31, 2018	Jul. 31, 2019	Jul. 31, 2018	Jan. 31, 2019
UNALLOCATED RESERVE AND DISTRIBUTIONS
Distribution declared per unit (Note 3) (in dollars per unit)	$ 0.21	$ 0.2100	$ 0.2200	$ 1.1000	$ 0.6700
Unallocated Cash and Securities portion of Unallocated Reserve
Cash and U.S. Government securities		$ 16,937,387		$ 16,937,387		$ 33,004,122
Distribution payable		(2,755,202)		(2,755,202)		(18,236,814)
Unallocated cash and U.S. Government securities		14,182,185		14,182,185		$ 14,767,308
Reconciliation of Trust's Unallocated Reserve
Beginning Balance		10,039,171	$ 11,018,521	16,805,692	$ 10,606,678
Net income		13,911,687	18,871,455	18,821,975	25,187,303
Distributions declared		(2,755,202)	(2,886,401)	(14,432,011)	(8,790,406)
Ending Balance		$ 21,195,656	$ 27,003,575	$ 21,195,656	$ 27,003,575
Distribution declared per unit		$ 0.2100	$ 0.2200	$ 1.1000	$ 0.6700
Unallocated Reserve
Reconciliation of Trust's Unallocated Reserve
Beginning Balance		$ 10,039,168	$ 11,018,518	$ 16,805,689	$ 10,606,675
Net income		13,911,687	18,871,455	18,821,975	25,187,303
Distributions declared		(2,755,202)	(2,886,401)	(14,432,011)	(8,790,406)
Ending Balance		21,195,653	27,003,572	21,195,653	27,003,572
Trust Corpus
Reconciliation of Trust's Unallocated Reserve
Beginning Balance		3	3	3	3
Ending Balance		$ 3	$ 3	$ 3	$ 3