Acquisitions - Additional Information (Detail) (USD $)	12 Months Ended
	May 31, 2014	May 31, 2013
TWB
Business Acquisition [Line Items]
Cash consideration for acquired entity	$ 17,869,000
Fair value inputs, control premium	10.00%
Net sales	319,542,000
Earnings before income taxes	22,991,000
Proforma net sales	3,180,428,000	2,956,309,000
TWB | Joint Venture Transactions
Business Acquisition [Line Items]
Cash consideration for acquired entity	17,869,000
Business Acquisition, Date of Acquisition Agreement	Jul. 31, 2013
Percentage of additional interest acquired by the company	10.00%
Percent of controlling interest by the company	55.00%
Previously held percentage of ownership interest	45.00%
Recognized gain from previously held equity interest	11,000,000
Palmer Mfg. And Tank, Inc
Business Acquisition [Line Items]
Cash consideration for acquired entity	113,479,000
Business Acquisition, Date of Acquisition Agreement	Apr. 09, 2013
Steffes
Business Acquisition [Line Items]
Cash consideration for acquired entity	28,874,000
Business Acquisition, Date of Acquisition Agreement	Mar. 27, 2014
Total consideration for acquired entity	28,290,000
Worthington Aritas
Business Acquisition [Line Items]
Business Acquisition, Date of Acquisition Agreement	Jan. 24, 2014
Percentage of additional interest acquired by the company	75.00%
Percent of interest owned by noncontrolling interest	25.00%
Total consideration for acquired entity	35,325,000
Contingent consideration estimated fair value	404,000
Additional consideration to the former owners	2,000,000
Earnings before interest, taxes, depreciation and amortization	5,000,000
Acquisition related costs	1,520,000
Westerman, Inc
Business Acquisition [Line Items]
Cash consideration for acquired entity	62,749,000
Business Acquisition, Date of Acquisition Agreement	Sep. 17, 2012
Percentage of additional interest acquired by the company	100.00%
Assumption of debt related to acquisition, current	$ 7,251,000