Revenues from External Customers and Long-Lived Assets, by Geographical Areas (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	May. 31, 2015	Feb. 28, 2015	Nov. 30, 2014	Aug. 31, 2014	May. 31, 2014	Feb. 28, 2014	Nov. 30, 2013	Aug. 31, 2013	May. 31, 2015	May. 31, 2014	May. 31, 2013
Revenues:
Total revenues	$ 60,413	$ 56,342	$ 59,703	$ 61,871	$ 61,077	$ 62,016	$ 57,876	$ 60,168	$ 238,329	$ 241,137	$ 248,731
Net Long Lived Assets:
Total net long-lived assets	244,791				235,010				244,791	235,010	248,682
UNITED STATES
Revenues:
Total revenues									200,323	203,806	211,745
Net Long Lived Assets:
Total net long-lived assets	197,514				188,343				197,514	188,343	198,956
Non-United States [Member]
Revenues:
Total revenues									38,006	37,331	36,986
Net Long Lived Assets:
Total net long-lived assets	$ 47,277				$ 46,667				$ 47,277	$ 46,667	$ 49,726