Consolidated Statements Of Shareholders' Equity (USD $) In Thousands	Total	Common stock	Treasury stock	Additional Paid in Capital	Non Controlling Interest	Retained Earnings	Accumulated Other Comprehensive Income (Loss)
Beginning balance at May. 31, 2010	$ 165,192	$ 5,696		$ 69,380		$ 92,553	$ (2,437)
Beginning balance (in shares) at May. 31, 2010		18,988
Net income	26,624					26,624
Foreign currency translation adjustment, net of tax	6,981						6,981
Foreign currency hedge, net of tax	(1,586)						(1,586)
Purchase of treasury stock (in shares)			(90)
Purchase of treasury stock	(1,344)		(1,344)
Acquisition of Quest Integrity (in shares)		186
Acquisition of Quest Integrity	7,552	56		2,579	4,917
Comprehensive income attributable to non-controlling interest	(66)				66	(39)	(27)
Non-cash compensation	4,993			4,993
Vesting of stock awards (in shares)		85
Vesting of stock awards	(433)	25		(458)
Exercise of stock options (in shares)	329	312
Exercise of stock options	2,232	94		2,138
Tax benefit of exercise of stock options	551			551
Correction of tax error (see Note 8)	(1,316)			(1,316)
Ending balance at May. 31, 2011	209,446	5,871	(1,344)	77,867	4,983	119,138	2,931
Ending balance (in shares) at May. 31, 2011		19,571	(90)
Net income	33,068					33,068
Foreign currency translation adjustment, net of tax	(7,018)						(7,018)
Foreign currency hedge, net of tax	1,457						1,457
Comprehensive income attributable to non-controlling interest	(114)				114	(157)	43
Non-cash compensation	4,386			4,386
Vesting of stock awards (in shares)		106
Vesting of stock awards	(868)	31		(899)
Exercise of stock options (in shares)	278	278
Exercise of stock options	2,997	83		2,914
Tax benefit of exercise of stock options	1,533			1,533
Ending balance at May. 31, 2012	245,001	5,985	(1,344)	85,801	5,097	152,049	(2,587)
Ending balance (in shares) at May. 31, 2012		19,955	(90)
Net income	32,714					32,714
Foreign currency translation adjustment, net of tax	1,200						1,200
Foreign currency hedge, net of tax	(393)						(393)
Comprehensive income attributable to non-controlling interest	(287)				287	(278)	(9)
Non-cash compensation	3,931			3,931
Vesting of stock awards (in shares)		124
Vesting of stock awards	(1,534)	38		(1,572)
Exercise of stock options (in shares)	509	509
Exercise of stock options	8,275	153		8,122
Tax benefit of exercise of stock options	2,996			2,996
Ending balance at May. 31, 2013	$ 292,190	$ 6,176	$ (1,344)	$ 99,278	$ 5,384	$ 184,485	$ (1,789)
Ending balance (in shares) at May. 31, 2013		20,588	(90)