Consolidated Statements of Equity - USD ($) $ in Thousands	Total	PSI Energy Solutions, LLC	DHybrid Systems Llc	Common Shares	Additional Paid-in Capital	Accumulated Other Comprehensive Income (Loss), Net of Tax	Retained Earnings	Total	Noncontrolling Interest	Noncontrolling Interest PSI Energy Solutions, LLC	Noncontrolling Interest DHybrid Systems Llc
Balance at May. 31, 2012	$ 747,437				$ 192,338	$ (20,387)	$ 525,223	$ 697,174	$ 50,263
Balance (in shares) at May. 31, 2012				67,906,369
Net earnings	136,835						136,442	136,442	393
Other comprehensive income (loss)	8,364					8,351		8,351	13
Common shares issued, net of withholding tax (in shares)				2,771,042
Common shares issued, net of withholding tax	37,914				37,914			37,914
Stock-based compensation	17,829				17,829			17,829
Purchases and retirement of common shares (in shares)				(925,000)
Purchases and retirement of common shares	(30,417)				(3,217)		(27,200)	(30,417)
Payments to noncontrolling interests	(9,254)								(9,254)
Cash dividends declared ($0.52 per share in 2013, $0.60 per share in 2014 and $0.72 per share in 2015)	(36,471)						(36,471)	(36,471)
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
Acquisitions		$ 84,144								$ 84,144
Common shares issued, net of withholding tax (in shares)				1,036,573
Common shares issued, net of withholding tax	4,618				4,618			4,618
Stock-based compensation	$ 25,651				25,651			25,651
Purchases and retirement of common shares (in shares)	(3,380,500)			(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 ($0.52 per share in 2013, $0.60 per share in 2014 and $0.72 per share in 2015)	(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)
Acquisitions			$ 4,082								$ 4,082
Common shares issued, net of withholding tax (in shares)				909,181
Common shares issued, net of withholding tax	2,910				2,910			2,910
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 ($0.52 per share in 2013, $0.60 per share in 2014 and $0.72 per share in 2015)	(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