Consolidated Statements of Shareholders' Equity (Parenthetical) - $ / shares	3 Months Ended		6 Months Ended
	Nov. 30, 2018	Nov. 30, 2017	Nov. 30, 2018	Nov. 30, 2017
Statement of Stockholders' Equity [Abstract]
Dividends declared per common share (in dollars per share)	$ 0.22	$ 0.20	$ 0.42	$ 0.38
Dividends declared per preferred share (in dollars per share)	$ 0.00	$ 0.00	$ 0.10	$ 0.10