Summary of Significant Accounting Policies - Additional Information (Detail)	12 Months Ended
	May 31, 2017 USD ($) JointVentures Entity Facility Segment Customer	May 31, 2016 USD ($)	May 31, 2015 USD ($)
Significant Accounting Policies [Line Items]
Number of joint ventures | JointVentures	11
Tax amount related to purchase of noncontrolling interest and its carrying value in dHybrid	$ 539,000
Lower of cost or market adjustment			$ 1,716,000
Derivative financial instruments, credit losses	$ 0
Number of manufacturing facilities operated | Facility	30
Number of reportable segments | Segment	3
Returns and allowances increase (decrease)	$ 685,000
Returns and Allowances	6,738,000
Allowance for doubtful accounts increase (decrease)	(1,135,000)
Receivables, allowances	3,444,000	$ 4,579,000
Depreciation Expenses	73,268,000	68,886,000	64,666,000
Advertising Expenses	14,822,000	13,970,000	11,153,000
Provision (benefit) for income taxes	79,190,000	58,987,000	$ 25,772,000
Additional Paid-in Capital
Significant Accounting Policies [Line Items]
Purchase of noncontrolling interest and its carrying value in dHybrid	935,000
Accounting Standards Update 2015-03
Significant Accounting Policies [Line Items]
Debt issuance cost	2,146,000	2,491,000
Adjustments for New Accounting Pronouncement
Significant Accounting Policies [Line Items]
Provision (benefit) for income taxes	$ (16,243,000)	$ (3,178,000)
Amended accounting guidance, description	Income Tax Accounting – The amended accounting guidance requires all excess tax benefits and tax deficiencies to be recognized as an income tax benefit or expense on a prospective basis in the period of adoption. The adoption of this provision of the amended accounting guidance resulted in the recognition of excess tax benefits of $16,243,000 and $3,178,000 in income tax expense, rather than in paid-in capital, during fiscal 2017 and fiscal 2016, respectively. As the adoption was on a prospective basis, fiscal 2015 has not been restated.
Building and Improvements | Minimum
Significant Accounting Policies [Line Items]
Property, plant and equipment, estimated useful life	10 years
Building and Improvements | Maximum
Significant Accounting Policies [Line Items]
Property, plant and equipment, estimated useful life	40 years
Machinery and Equipment | Minimum
Significant Accounting Policies [Line Items]
Property, plant and equipment, estimated useful life	3 years
Machinery and Equipment | Maximum
Significant Accounting Policies [Line Items]
Property, plant and equipment, estimated useful life	20 years
Largest Customer
Significant Accounting Policies [Line Items]
Number of customers | Customer	10
Net Sales | Product Concentration Risk
Significant Accounting Policies [Line Items]
Concentration risk percentage	43.00%	42.00%	38.00%
Net Sales | Foreign Operations
Significant Accounting Policies [Line Items]
Concentration risk percentage	7.00%	6.00%	4.00%
Net Sales | Customer Concentration Risk | Largest Customer
Significant Accounting Policies [Line Items]
Concentration risk percentage	9.00%
Net Sales | Customer Concentration Risk | Ten Largest Customers
Significant Accounting Policies [Line Items]
Concentration risk percentage	34.00%
Net Earnings | Foreign Operations
Significant Accounting Policies [Line Items]
Concentration risk percentage	4.00%	8.00%	(4.00%)
Net Assets, Segment | Foreign Operations
Significant Accounting Policies [Line Items]
Concentration risk percentage	11.00%	12.00%
Workforce Subject to Collective Bargaining Arrangements | Labor Force Concentration Risk [Member]
Significant Accounting Policies [Line Items]
Concentration risk percentage	9.00%
Joint Venture Transactions
Significant Accounting Policies [Line Items]
Number of joint ventures | Entity	5
Number of manufacturing facilities operated | Facility	50
Spartan | Joint Venture Transactions
Significant Accounting Policies [Line Items]
Percent of controlling interest by the Company	52.00%
TWB | Joint Venture Transactions
Significant Accounting Policies [Line Items]
Percent of controlling interest by the Company	55.00%
Worthington Aritas | Joint Venture Transactions
Significant Accounting Policies [Line Items]
Percent of controlling interest by the Company	75.00%
WEI | Joint Venture Transactions
Significant Accounting Policies [Line Items]
Percent of controlling interest by the Company	75.00%
Worthington Specialty Processing | Joint Venture Transactions
Significant Accounting Policies [Line Items]
Percent of controlling interest by the Company	51.00%