Condensed Statements of Income (USD $)	3 Months Ended		9 Months Ended
	Oct. 31, 2011	Oct. 31, 2010	Oct. 31, 2011	Oct. 31, 2010
Revenues
Royalty income	$ 13,967,426	$ 11,574,496	$ 27,576,049	$ 27,790,642
Interest income	979	1,817	3,669	12,478
Total revenues	13,968,405	11,576,313	27,579,718	27,803,120
Expenses	212,068	179,747	627,836	612,295
Net income	$ 13,756,337	$ 11,396,566	$ 26,951,882	$ 27,190,825
Number of units outstanding (in units)	13,120,010	13,120,010	13,120,010	13,120,010
Net income per unit (Note 2) (in dollars per unit)	$ 1.0485	$ 0.8686	$ 2.0543	$ 2.0725
Distributions declared per unit (Note 3) (in dollars per unit)	$ 1.1200	$ 0.9100	$ 1.7700	$ 1.8350