Income Taxes - Components of Deferred Income Taxes (Details) - USD ($) $ in Thousands	May 31, 2019	May 31, 2018	May 31, 2017
Deferred tax assets:
Allowance for doubtful accounts	$ 9,495	$ 8,209
Inventory obsolescence	9,257	10,425
Insurance and contingencies	45,339	43,482
Stock-based compensation	77,697	64,376
Net operating loss and foreign related carry-forwards	9,109	12,882
Treasury locks	5,806	0
Deferred compensation and other	48,922	37,319
Deferred tax assets, gross	205,625	176,693
Valuation allowance	(7,308)	(11,302)	$ (18,088)
Deferred tax assets, net	198,317	165,391
Deferred tax liabilities:
Uniform and other rental items in service	194,939	170,157
Property and equipment	159,186	126,273
Service contracts and other intangible assets	210,531	215,455
Treasury locks	0	4,185
Capitalized contract costs	70,228	0
State taxes and other	1,612	1,902
Deferred tax liabilities	636,496	517,972
Net deferred tax liability	$ 438,179	$ 352,581