Condensed Balance Sheets (Parenthetical)	Oct. 31, 2012	Jan. 31, 2012
Condensed Balance Sheets
Certificate of beneficial interest of land trust, units	13,120,010	13,120,010

Transferable units distributed to shareholders of Mesabi Iron Company as beneficial interest in Mesabi Trust.

No definition available.

Name:	msb_CertificateOfBeneficialInterestUnits
Namespace Prefix:	msb_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant