UNALLOCATED RESERVE AND DISTRIBUTIONS (Details) (USD $)	3 Months Ended		6 Months Ended
	Jul. 31, 2013	Jul. 31, 2012	Jul. 31, 2013	Jul. 31, 2012	Jan. 31, 2013
UNALLOCATED RESERVE AND DISTRIBUTIONS
Cash and U.S. Government securities	$ 6,757,004		$ 6,757,004		$ 7,371,331
Distribution payable	6,035,205		6,035,205		6,428,805
Unallocated cash and U.S. Government securities	721,799		721,799		942,526
Reconciliation of unallocated reserve
Unallocated reserve at the beginning of the period			1,182,222
Net income	7,624,780	10,873,286	9,827,169	14,243,178
Distributions declared			(7,084,806)
Unallocated reserve at the end of the period	3,924,585		3,924,585
Within a range of not less
UNALLOCATED RESERVE AND DISTRIBUTIONS
Unallocated cash and U.S. Government securities	500,000		500,000
Within a range of not more
UNALLOCATED RESERVE AND DISTRIBUTIONS
Unallocated cash and U.S. Government securities	$ 1,000,000		$ 1,000,000