UNALLOCATED RESERVE AND DISTRIBUTIONS (Details) (USD $)	3 Months Ended		9 Months Ended
	Oct. 31, 2013	Oct. 31, 2012	Oct. 31, 2013	Oct. 31, 2012	Jan. 31, 2013
UNALLOCATED RESERVE AND DISTRIBUTIONS
Cash and U.S. Government securities	$ 7,606,241		$ 7,606,241		$ 7,371,331
Distribution payable	6,691,205		6,691,205		6,428,805
Unallocated cash and U.S. Government securities	915,036		915,036		942,526
Reconciliation of unallocated reserve
Unallocated reserve at the beginning of the period			1,182,222
Net income	6,136,515	11,624,026	15,963,684	25,867,203
Distributions declared			(13,776,011)
Unallocated reserve at the end of the period	3,369,895		3,369,895
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