Condensed Statements of Income (USD $)	3 Months Ended		6 Months Ended
	Jul. 31, 2012	Jul. 31, 2011	Jul. 31, 2012	Jul. 31, 2011
Revenues
Royalty income	$ 11,059,872	$ 10,332,035	$ 14,752,993	$ 13,608,623
Interest income	352	1,231	677	2,690
Total revenues	11,060,224	10,333,266	14,753,670	13,611,313
Expenses	186,938	200,981	510,492	415,768
Net income	$ 10,873,286	$ 10,132,285	$ 14,243,178	$ 13,195,545
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)	$ 0.8288	$ 0.7723	$ 1.0856	$ 1.0058
Distributions declared per unit (Note 3) (in dollars per unit)	$ 0.6400	$ 0.6000	$ 0.7050	$ 0.6500