Income Taxes - Earnings before Income Taxes (Detail) - USD ($) $ in Thousands		12 Months Ended
		May 31, 2018	May 31, 2017	May 31, 2016
Income Tax Disclosure [Abstract]
United States based operations		$ 177,088	$ 266,222	$ 180,467
Non – United States based operations		31,982	30,905	36,148
Earnings before income taxes		209,070	297,127	216,615
Net earnings attributable to noncontrolling interests	[1]	6,056	13,422	13,913
Earnings before income taxes attributable to controlling interest		$ 203,014	$ 283,705	$ 202,702

[1] Net earnings attributable to noncontrolling interests are not taxable to Worthington.