Stock-Based Compensation - Additional Information (Detail) - USD ($)	12 Months Ended
	May 31, 2017	May 31, 2016	May 31, 2015	May 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock authorized for issuance	3,797,139
Stock based compensation expense, pre tax	$ 14,349,000	$ 15,836,000	$ 17,916,000
Stock based compensation expense, after tax	9,112,000	$ 10,056,000	$ 11,500,000
Unrecognized compensation cost	$ 18,012,000
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
Total intrinsic value of stock options exercised	$ 18,989,000
Cash received from the exercise of stock options	11,676,000
Tax benefit realized from share-based payment awards	$ 16,243,000
Non-Qualified Stock Options | 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 | 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 | 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]
Service-based restricted common shares granted to employees cliff vesting period	3 years
Restricted common shares, granted	525,000	217,000	240,000
Restricted common shares, fair value per share	$ 42.28	$ 29.49	$ 40.05
Unrecognized compensation cost	$ 19,841,000	$ 5,800,000	$ 8,660,000
Restricted common shares, outstanding	865,000	698,000	635,000	573,000
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			$ 1,603,000
Restricted common shares, outstanding	25,000