Condensed Statements of Income (USD $)	3 Months Ended		9 Months Ended
	Oct. 31, 2012	Oct. 31, 2011	Oct. 31, 2012	Oct. 31, 2011
Revenues
Royalty income	$ 11,814,026	$ 13,967,426	$ 26,567,019	$ 27,576,049
Interest income	394	979	1,071	3,669
Total revenues	11,814,420	13,968,405	26,568,090	27,579,718
Expenses	190,394	212,068	700,887	627,836
Net income	$ 11,624,026	$ 13,756,337	$ 25,867,203	$ 26,951,882
Number of units outstanding	13,120,010	13,120,010	13,120,010	13,120,010
Net income per unit (Note 2) (in dollars per unit)	$ 0.8860	$ 1.0485	$ 1.9716	$ 2.0543
Distributions declared per unit (Note 3) (in dollars per unit)	$ 1.1300	$ 1.1200	$ 1.8350	$ 1.7700