Consolidated Statements Of Shareholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Treasury Stock	Additional Paid in Capital	Noncontrolling Interest	Retained Earnings	Accumulated Other Comprehensive Income (Loss)
Beginning balance (in shares) at May. 31, 2013		20,588,000	(90,000)
Beginning balance at May. 31, 2013	$ 292,190	$ 6,176	$ (1,344)	$ 99,278	$ 5,384	$ 184,485	$ (1,789)
Net income (loss)	30,149					30,149
Foreign currency translation adjustment, net of tax	(400)						(400)
Foreign currency hedge, net of tax	(490)						(490)
Comprehensive income attributable to noncontrolling interest	(294)				294	(294)
Non-cash compensation	4,239			4,239
Vesting of stock awards (in shares)		117,000
Vesting of stock awards	(1,710)	$ 34		(1,744)
Tax effect of share-based payment arrangements	$ 1,131			1,131
Exercise of stock options (in shares)	232,000	232,000
Exercise of stock options	$ 5,270	$ 70		5,200
Purchase of treasury stock (in shares)			(369,000)
Purchase of treasury stock	(13,334)		$ (13,334)
Retirement of treasury stock, in shares		459,000	459,000
Retirement of treasury stock		$ (138)	$ 14,678	(2,232)		(12,308)
Ending balance (in shares) at May. 31, 2014		20,478,000
Ending balance at May. 31, 2014	317,045	$ 6,142		105,872	5,678	202,032	(2,679)
Net income (loss)	40,497					40,497
Foreign currency translation adjustment, net of tax	(13,263)						(13,263)
Foreign currency hedge, net of tax	2,333						2,333
Comprehensive income attributable to noncontrolling interest	(356)				356	(427)	71
Non-cash compensation	4,838			4,838
Vesting of stock awards (in shares)		106,000
Vesting of stock awards	(1,775)	$ 33		(1,808)
Tax effect of share-based payment arrangements	$ 3,034			3,034
Exercise of stock options (in shares)	326,000	325,000
Exercise of stock options	$ 3,804	$ 98		3,706
Purchase of treasury stock	(21,100)
Purchase of treasury stock (in shares)			(547,000)
Purchase of treasury stock	(21,138)		$ (21,138)
Ending balance (in shares) at May. 31, 2015		20,909,000	(547,000)
Ending balance at May. 31, 2015	335,375	$ 6,273	$ (21,138)	115,642	6,034	242,102	(13,538)
Net income (loss)	8,878					8,878
Foreign currency translation adjustment, net of tax	(4,898)						(4,898)
Foreign currency hedge, net of tax	62						62
Comprehensive income attributable to noncontrolling interest	0
Purchase of non-controlling interest, shares		728,000
Purchase of noncontrolling interest	(5,934)	$ 218		(118)	$ (6,034)
Non-cash compensation	3,522			3,522
Vesting of stock awards (in shares)		89,000
Vesting of stock awards	(1,375)	$ 27		(1,402)
Tax effect of share-based payment arrangements	$ 374			374
Exercise of stock options (in shares)	109,000	111,000
Exercise of stock options	$ 2,142	$ 34		2,108
Ending balance (in shares) at Dec. 31, 2015		21,837,000	(547,000)
Ending balance at Dec. 31, 2015	338,146	$ 6,552	$ (21,138)	120,126		250,980	(18,374)
Net income (loss)	(12,676)					(12,676)
Foreign currency translation adjustment, net of tax	(2,498)						(2,498)
Foreign currency hedge, net of tax	300						300
Change in defined benefit pension plan net actuarial loss, net of tax	(8,428)						(8,428)
Comprehensive income attributable to noncontrolling interest	0
Non-cash compensation	7,313			7,313
Vesting of stock awards (in shares)		142,000
Vesting of stock awards	(1,709)	$ 40		(1,749)
Tax effect of share-based payment arrangements	(535)			(535)
Issuance of common stock in Furmanite acquisition and conversion of Furmanite share-based awards (in shares)		8,208,000
Issuance of common stock in Furmanite acquisition and conversion of Furmanite share-based awards	$ 211,530	$ 2,462		209,068
Exercise of stock options (in shares)	251,000	251,000
Exercise of stock options	$ 5,903	$ 75		5,828
Issuance of common stock, in shares	167,931	168,000
Issuance of common stock	$ 5,934	$ 50		5,884
Purchase of treasury stock, in shares	(274,110)		(274,000)
Purchase of treasury stock	$ (7,593)		$ (7,593)
Retirement of treasury stock, in shares	821,087	821,000	821,000
Retirement of treasury stock	$ 0	$ (245)	$ 28,731	(9,129)		(19,357)
Other	(50)			(50)
Ending balance (in shares) at Dec. 31, 2016		29,785,000	0
Ending balance at Dec. 31, 2016	$ 535,637	$ 8,934	$ 0	$ 336,756		$ 218,947	$ (29,000)