UNALLOCATED RESERVE AND DISTRIBUTIONS (Details) (USD $)	3 Months Ended		9 Months Ended
	Oct. 31, 2012	Oct. 31, 2011	Oct. 31, 2012	Oct. 31, 2011	Jan. 31, 2012
UNALLOCATED RESERVE AND DISTRIBUTIONS
Cash and U.S. Government securities	$ 15,644,899		$ 15,644,899		$ 10,727,290
Distribution payable	(14,825,611)		(14,825,611)		(9,971,208)
Unallocated cash and U.S. Government securities	819,288		819,288		756,082
Reconciliation of unallocated reserve
Unallocated reserve at the beginning of the period			1,031,508
Net income	11,624,026	13,756,337	25,867,203	26,951,882
Distributions declared			(24,075,218)
Unallocated reserve at the end of the period	2,823,493		2,823,493
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