Convertible Special Stock (Details) - USD ($)	3 Months Ended		9 Months Ended		12 Months Ended
	May 31, 2016	May 31, 2015	May 31, 2016	May 31, 2015	Aug. 31, 2015	May 04, 2015
Class of Stock [Line Items]
Convertible special stock, shares authorized						125,000
Convertible special stock, dividend rate, percentage						6.00%
Issuances of convertible special stock, gross		$ 125,000,000
Convertible special stock, shares issued						125,000
Convertible special stock, no par value	$ 120,289,000		$ 120,289,000		$ 120,289,000
Payment of financing and stock issuance costs						$ 4,700,000
Convertible special stock, shares converted to common shares			0		0
Convertible special stock dividends	$ 1,875,000	$ 563,000	$ 5,625,000	$ 563,000