Acquisitions - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	May 31, 2016	May 31, 2015
Worthington Specialty Processing
Business Acquisition [Line Items]
Previously held percentage of ownership interest	51.00%
Business acquisition, date of acquisition agreement	Mar. 01, 2016
Gain on re-measurement of ownership interest to fair value	$ 6,877
Estimated fair value of previously held interest	$ 32,375
Worthington Specialty Processing | Joint Venture Transactions
Business Acquisition [Line Items]
Percent of controlling interest by the Company	51.00%
Worthington Specialty Processing | Joint Venture Transactions | United States Steel Corporation
Business Acquisition [Line Items]
Percent of ownership interest by noncontrolling owner	49.00%
CryoScience
Business Acquisition [Line Items]
Business acquisition, date of acquisition agreement	Dec. 07, 2015
Total consideration for acquired entity	$ 30,584
Business acquisition, estimated working capital deficit adjustment	772
Cash paid at the closing date	$ 31,356
NetBraze, LLC
Business Acquisition [Line Items]
Business acquisition, date of acquisition agreement	Jan. 15, 2016
Total consideration for acquired entity	$ 3,390
Business acquisition, contingent consideration estimated fair value	540
Business acquisition, working capital	1,565
Business acquisition, fixed assets	$ 1,825
Rome Strip Steel
Business Acquisition [Line Items]
Business acquisition, date of acquisition agreement		Jan. 16, 2015
Total consideration for acquired entity		$ 54,495
Business acquisition, estimated working capital deficit adjustment		817
Cash paid at the closing date		$ 55,312
DHybrid Systems LLC
Business Acquisition [Line Items]
Percent of ownership interest by noncontrolling owner		20.41%
Business acquisition, date of acquisition agreement		Oct. 20, 2014
Total consideration for acquired entity		$ 15,918
Cash paid at the closing date		$ 11,939
Percentage of additional interest acquired by the company		79.59%
Contingent consideration estimated fair value		$ 3,979
Contingent consideration to be paid upon achievement of net sales and gross margin thresholds		3,979
Cumulative net sales threshold beginning January 1, 2013		$ 20,000
Gross margin threshold		50.00%
MEF
Business Acquisition [Line Items]
Business acquisition, date of acquisition agreement		Aug. 01, 2014
Cash paid at the closing date		$ 38,441
JRE
Business Acquisition [Line Items]
Business acquisition, date of acquisition agreement		Jul. 31, 2014
Cash paid at the closing date		$ 1,571