Earnings before Income Taxes (Detail) - USD ($) $ in Thousands		12 Months Ended
		May. 31, 2015	May. 31, 2014	May. 31, 2013
Schedule of Income Before Income Tax [Line Items]
United States based operations		$ 104,732	$ 210,783	$ 190,942
Non - United States based operations		8,296	6,718	10,358
Earnings before income taxes		113,028	217,501	201,300
Less: Net earnings attributable to noncontrolling interests	[1]	10,471	8,852	393
Earnings before income taxes attributable to controlling interest		$ 102,557	$ 208,649	$ 200,907

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