Condensed Statements of Income (USD $)	3 Months Ended		6 Months Ended
	Jul. 31, 2011	Jul. 31, 2010	Jul. 31, 2011	Jul. 31, 2010
Revenues
Royalty income	$ 10,332,035	$ 11,228,415	$ 13,608,623	$ 16,216,146
Interest income	1,231	5,565	2,690	10,661
Total revenues	10,333,266	11,233,980	13,611,313	16,226,807
Expenses	200,981	224,686	415,768	432,548
Net income	$ 10,132,285	$ 11,009,294	$ 13,195,545	$ 15,794,259
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)	$ 0.7723	$ 0.8391	$ 1.0058	$ 1.2038
Distributions declared per unit (Note 3) (in dollars per unit)	$ 0.6000	$ 0.8000	$ 0.6500	$ 0.9250