Income Taxes - Components of Deferred Income Taxes (Details) - USD ($) $ in Thousands	May 31, 2020	May 31, 2019	May 31, 2018
Deferred tax assets:
Allowance for doubtful accounts	$ 14,718	$ 9,495
Inventory obsolescence	13,744	9,257
Insurance reserves	45,197	45,339
Stock-based compensation	78,802	77,697
Net operating loss and foreign related carry-forwards	7,657	9,109
Treasury locks	39,046	5,806
Operating lease liabilities	42,191	0
Deferred compensation and other	73,562	48,922
Deferred tax assets, gross	314,917	205,625
Valuation allowance	(6,411)	(7,308)	$ (11,302)
Deferred tax assets, net	308,506	198,317
Deferred tax liabilities:
Uniform and other rental items in service	189,787	194,939
Property and equipment	177,664	159,186
Service contracts and other intangible assets	207,610	210,531
Capitalized contract costs	77,741	70,228
Operating lease right-of-use assets	42,191	0
State taxes and other	2,092	1,612
Deferred tax liabilities	697,085	636,496
Net deferred tax liability	$ 388,579	$ 438,179