ROYALTY AGREEMENT, UNALLOCATED RESERVE AND DISTRIBUTIONS (Details) - USD ($)		3 Months Ended		6 Months Ended
	Jul. 13, 2018	Jul. 31, 2018	Jul. 31, 2017	Jul. 31, 2018	Jul. 31, 2017	Jan. 31, 2018
UNALLOCATED RESERVE AND DISTRIBUTIONS
Distribution declared or paid (in dollars per unit)	$ 0.22	$ 0.2200	$ 0.1600	$ 0.6700	$ 0.7100
Unallocated Cash and Securities portion of Unallocated Reserve
Cash and U.S. Government securities		$ 18,098,799		$ 18,098,799		$ 24,112,286
Distribution payable		(2,886,402)		(2,886,402)		(15,481,612)
Unallocated cash and U.S. Government securities		15,212,397		15,212,397		$ 8,630,674
Reconciliation of Trust's Unallocated Reserve
Unallocated Reserve at the beginning of the period				10,606,675
Net income		18,871,455	$ 13,996,954	25,187,303	$ 18,468,879
Distributions declared				(8,790,406)
Unallocated Reserve at the end of the period		$ 27,003,572		$ 27,003,572