Income Taxes - Reconciliation of Federal Statutory Corporate Income Tax Rate to Total Tax Provision (Detail)		5 Months Ended	7 Months Ended	12 Months Ended
		May 31, 2018	Dec. 31, 2017	May 31, 2018	May 31, 2017	May 31, 2016
Income Tax Disclosure [Abstract]
Federal statutory income tax rate		21.00%	35.00%	29.20%	35.00%	35.00%
State and local income taxes, net of federal tax benefit				2.30%	1.50%	1.50%
Non-U.S. income taxes at other than federal statutory rate				(1.40%)	(1.40%)	(3.00%)
Qualified production activities deduction				(2.30%)	(1.90%)	(2.20%)
Impact of tax reform	[1]			(15.40%)
Worthington Aritas write down				(4.80%)
Excess benefit related to share-based payment awards				(2.00%)	(5.70%)	(1.60%)
AMTROL acquisition				(1.90%)
Other				0.30%	0.40%	(0.60%)
Effective tax rate attributable to controlling interest				4.00%	27.90%	29.10%

[1] Amount reflects the impact of the re-measurement of the Company’s deferred tax balances at the lower federal statutory corporate income tax rate, net of the mandatory deemed repatriation tax on unremitted foreign earnings.