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Financial Instruments and Credit Risk Concentrations
3 Months Ended
Oct. 31, 2019
Fair Value Disclosures [Abstract]  
Financial Instruments and Credit Risk Concentrations
4. Financial Instruments and Credit Risk Concentrations:
          
Financial instruments that are potentially subject to concentrations of credit risk consist principally of marketable securities, cash and cash equivalents and receivables. Marketable securities and cash and cash equivalents are placed with multiple financial institutions and multiple instruments to minimize risk. No assurance can be made that such financial institutions and instruments will minimize all such risk.
 
The Company derives rental income from approximately fifty tenants, of which one tenant accounted for 15.98%, another tenant accounted for 15.77% and a third tenant accounted for 12.25% of rental income during the three months ended October 31, 2019. The three months ended October 31, 2018 had one tenant account for 16.16%, another tenant account for 13.81% and a third tenant account for 11.95% of rental income. No other tenant accounted for more than 10% of rental income during the same periods.