Supplemental Financial Statement Information - AFS Securities (Details)	3 Months Ended
Aug. 31, 2017 shares
Investments
Shares of Centaur Media common stock sold	1,952,462

Represents the number of shares of common stock sold.

No definition available.

Name:	grif_InvestmentOwnedSharesSold
Namespace Prefix:	grif_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration