NET INCOME PER UNIT (Details) (USD $)	3 Months Ended
Apr. 30, 2015	Apr. 30, 2014	Jan. 31, 2015
NET INCOME PER UNIT
Accrued income receivable	$ 1,023,223msb_AccruedIncomeReceivable		$ 558,385msb_AccruedIncomeReceivable
Number of units outstanding	13,120,010	13,120,010

Royalty revenue and estimated price adjustments related to prior periods earned but not yet received by the entity on its mineral interests.

No definition available.

Name:	msb_AccruedIncomeReceivable
Namespace Prefix:	msb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant