Stock-Based Compensation - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	May 31, 2018	May 31, 2017	May 31, 2016	May 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock authorized for issuance	2,958,967
Stock based compensation expense, pre tax	$ 13,758	$ 14,349	$ 15,836
Stock based compensation expense, after tax	9,482	9,112	10,056
Unrecognized compensation cost	$ 14,312
Unrecognized compensation cost related to non-vested awards, expense period	3 years
Non-Qualified Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Purchase price percentage of fair market value on the date of grant for stock options	100.00%
Stock options expiration period	10 years
Stock based compensation expense, pre tax	$ 1,203	1,146	1,305
Total intrinsic value of stock options exercised	5,758
Cash received from the exercise of stock options	3,864
Tax benefit realized from share-based payment awards	$ 4,075
Non-Qualified Stock Options | First Anniversary | Issued Before June 30, 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options vesting percentage	20.00%
Non-Qualified Stock Options | First Anniversary | Issued On or After June 30, 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options vesting percentage	33.00%
Non-Qualified Stock Options | Second Anniversary | Issued Before June 30, 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options vesting percentage	20.00%
Non-Qualified Stock Options | Second Anniversary | Issued On or After June 30, 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options vesting percentage	33.00%
Non-Qualified Stock Options | Third Anniversary | Issued Before June 30, 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options vesting percentage	20.00%
Non-Qualified Stock Options | Third Anniversary | Issued On or After June 30, 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options vesting percentage	33.00%
Non-Qualified Stock Options | Fourth Anniversary | Issued Before June 30, 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options vesting percentage	20.00%
Non-Qualified Stock Options | Fifth Anniversary | Issued Before June 30, 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options vesting percentage	20.00%
Non-Qualified Stock Options | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Purchase price percentage of fair market value on the date of grant for stock options	100.00%
Service-Based Restricted Common Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock based compensation expense, pre tax	$ 7,605	$ 19,841	$ 5,800
Service-based restricted common shares granted to employees cliff vesting period	3 years
Restricted common shares, granted	176,000	525,000	217,000
Restricted common shares, fair value per share	$ 47.88	$ 42.28	$ 29.49
Restricted common shares, outstanding	796,000	865,000	698,000	635,000
Market-Based Restricted Common Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted common shares, granted				50,000
Common share awards vesting, minimum price per share				$ 60.00
Common share awards vesting, minimum consecutive days at stated price				30 days
Restricted common shares, fair value per share				$ 32.06
Unrecognized compensation cost				$ 1,603
Restricted common shares, outstanding	25,000
Restricted common shares, cancelled			25,000