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 (in shares) at May. 31, 2012		19,955,000	(90,000)
Beginning balance at May. 31, 2012	$ 245,001	$ 5,985	$ (1,344)	$ 85,801	$ 5,097	$ 152,049	$ (2,587)
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)		124,000
Vesting of stock awards	$ (1,534)	$ 38		(1,572)
Exercise of stock options (in shares)	509,000	509,000
Exercise of stock options	$ 8,275	$ 153		8,122
Tax benefit of exercise of stock options	2,996			2,996
Ending balance (in shares) at May. 31, 2013		20,588,000	(90,000)
Ending balance at May. 31, 2013	292,190	$ 6,176	$ (1,344)	99,278	5,384	184,485	(1,789)
Net income	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 non-controlling 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)
Exercise of stock options (in shares)	232,000	232,000
Exercise of stock options	$ 5,270	$ 70		5,200
Tax benefit of exercise of stock options	1,131			1,131
Purchase of treasury stock (in shares)			(369,000)
Purchase of treasury stock	(13,334)		$ (13,334)
Retirement of common stock (in shares)		(459,000)	459,000
Retirement of common 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	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 non-controlling 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)
Exercise of stock options (in shares)	326,000	325,000
Exercise of stock options	$ 3,804	$ 98		3,706
Tax benefit of exercise of stock options	3,034			3,034
Purchase of treasury stock (in shares)			(547,000)
Purchase of treasury stock	$ (21,138)		$ (21,138)
Retirement of common stock (in shares)	546,977
Retirement of common stock	$ (21,100)
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	8,878					8,878
Foreign currency translation adjustment, net of tax	(4,898)						(4,898)
Foreign currency hedge, net of tax	62						62
Purchase of non-controlling interest	(5,934)	$ 218		(118)	$ (6,034)
Purchase of non-controlling interest, shares		728,000
Non-cash compensation	3,522			3,522
Vesting of stock awards (in shares)		89,000
Vesting of stock awards	$ (1,375)	$ 27		(1,402)
Exercise of stock options (in shares)	109,000	111,000
Exercise of stock options	$ 2,142	$ 34		2,108
Tax benefit of exercise of stock options	374			374
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)