Income Taxes - Components of Deferred Income Taxes (Details) - USD ($) $ in Thousands	May 31, 2018	May 31, 2017	May 31, 2016
Deferred tax assets:
Allowance for doubtful accounts	$ 6,955	$ 7,707
Inventory obsolescence	8,668	16,096
Insurance and contingencies	36,727	54,489
Stock-based compensation	53,532	73,027
Net operating loss and foreign related carry-forwards	11,910	37,814
Deferred compensation and other	31,093	25,891
Deferred tax assets, gross	148,885	215,024
Valuation allowance	(11,302)	(18,088)	$ (17,047)
Deferred tax assets, net	137,583	196,936
Deferred tax liabilities:
Uniform and other rental items in service	143,580	210,766
Property and equipment	115,712	126,872
Service contracts and other intangible assets	183,000	290,049
Treasury locks	3,545	6,435
State taxes and other	44,327	32,142
Deferred tax liabilities	490,164	666,264
Net deferred tax liability	$ 352,581	$ 469,328