STATEMENTS OF UNALLOCATED RESERVE AND TRUST CORPUS (Parenthetical) - $ / shares	3 Months Ended
Jan. 31, 2016	Oct. 31, 2015	Jul. 31, 2015	Jan. 31, 2015	Oct. 31, 2014	Jan. 31, 2014	Oct. 31, 2013	Jul. 31, 2013
STATEMENTS OF UNALLOCATED RESERVE AND TRUST CORPUS
Distribution paid (in dollars per unit)	$ 0.00	$ 0.04	$ 0.00	$ 0.88	$ 0.32	$ 0.51	$ 0.46	$ 0.08
Distributions declared per unit (in dollars per unit)	$ 0.05			$ 0.64		$ 0.57

Cash dividends declared per unit by an entity during the period for all units of stock and subsequently paid within the following period.

No definition available.

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Namespace Prefix:	msb_
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Balance Type:	na
Period Type:	duration