Consolidated Statements of Equity - USD ($) $ in Thousands	Total	PSI Energy Solutions, LLC	DHybrid Systems LLC	Worthington Specialty Processing	Common Shares	Additional Paid-in Capital	Accumulated Other Comprehensive Loss, Net of Tax	Retained Earnings	Total	Noncontrolling Interests	Noncontrolling Interests PSI Energy Solutions, LLC	Noncontrolling Interests DHybrid Systems LLC	Noncontrolling Interests Worthington Specialty Processing
Balance at May. 31, 2013	$ 872,237					$ 244,864	$ (12,036)	$ 597,994	$ 830,822	$ 41,415
Balance (in shares) at May. 31, 2013					69,752,411
Net earnings	160,152							151,300	151,300	8,852
Other comprehensive income (loss)	9,083						8,455		8,455	628
Acquisition		$ 84,144									$ 84,144
Common shares issued, net of withholding tax	4,618					4,618			4,618
Common shares issued, net of withholding tax (in shares)					1,036,573
Stock-based compensation	25,651					25,651			25,651
Purchases and retirement of common shares (in shares)					(3,380,500)
Purchases and retirement of common shares	(128,218)					(12,523)		(115,695)	(128,218)
Payments to noncontrolling interests	(40,969)									(40,969)
Cash dividends declared ($0.60 per share in 2014, $0.72 per share in 2015, and $0.76 per share in 2016)	(41,816)							(41,816)	(41,816)
Balance at May. 31, 2014	944,882					262,610	(3,581)	591,783	850,812	94,070
Balance (in shares) at May. 31, 2014					67,408,484
Net earnings	87,256							76,785	76,785	10,471
Other comprehensive income (loss)	(49,620)						(47,123)		(47,123)	(2,497)
Acquisition			$ 4,082									$ 4,082
Common shares issued, net of withholding tax	2,910					2,910			2,910
Common shares issued, net of withholding tax (in shares)					909,181
Theoretical common shares in NQ plans	14,560					14,560			14,560
Stock-based compensation	$ 26,837					26,837			26,837
Purchases and retirement of common shares (in shares)	(4,176,187)				(4,176,187)
Purchases and retirement of common shares	$ (127,360)					(17,839)		(109,521)	(127,360)
Payments to noncontrolling interests	(15,189)									(15,189)
Cash dividends declared ($0.60 per share in 2014, $0.72 per share in 2015, and $0.76 per share in 2016)	(48,309)							(48,309)	(48,309)
Balance at May. 31, 2015	840,049					289,078	(50,704)	510,738	749,112	90,937
Balance (in shares) at May. 31, 2015					64,141,478
Net earnings	157,628							143,715	143,715	13,913
Other comprehensive income (loss)	24,866						22,139		22,139	2,727
Acquisition				$ 28,004									$ 28,004
Common shares issued, net of withholding tax	8,707					8,707			8,707
Common shares issued, net of withholding tax (in shares)					892,190
Theoretical common shares in NQ plans	960					960			960
Stock-based compensation	$ 16,534					16,534			16,534
Purchases and retirement of common shares (in shares)	(3,500,000)				(3,500,000)
Purchases and retirement of common shares	$ (99,847)					(16,295)		(83,552)	(99,847)
Payments to noncontrolling interests	(9,106)									(9,106)
Cash dividends declared ($0.60 per share in 2014, $0.72 per share in 2015, and $0.76 per share in 2016)	(47,949)							(47,949)	(47,949)
Balance at May. 31, 2016	$ 919,846					$ 298,984	$ (28,565)	$ 522,952	$ 793,371	$ 126,475
Balance (in shares) at May. 31, 2016					61,533,668