Equity - Additional Information (Detail) - USD ($) $ in Thousands		12 Months Ended
	Apr. 30, 2018	May 31, 2018	May 31, 2017	May 31, 2016	Sep. 27, 2017	Jun. 25, 2014
Class of Stock [Line Items]
Stock repurchase program additional number of shares authorized to be repurchased		0			6,828,855
Repurchase of common shares		$ 204,267	$ 0	$ 99,847
Purchases and retirement of common shares (in shares)		4,375,000		3,500,000
Deferred compensation obligation credited to common share option		$ 1,218	$ 1,259
Stock repurchase on June 25, 2014
Class of Stock [Line Items]
Common Stock remaining shares authorized for repurchase		6,500,000
Purchases of common shares (in shares)	10,000,000
Maximum | Stock repurchase on June 25, 2014
Class of Stock [Line Items]
Common Stock shares authorized for repurchase						10,000,000