Geographic Breakdown of Revenues and Total Assets (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 from External Customers and Long-Lived Assets [Line Items]
Total Revenues	$ 238,718	$ 174,589	$ 240,619	$ 188,121	$ 211,487	$ 163,236	$ 200,493	$ 174,311	$ 842,047	$ 749,527	$ 714,311
Total Assets	523,833				484,941				523,833	484,941	460,203
United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Total Revenues									625,044	540,967	508,928
Total Assets	399,173				353,624				399,173	353,624	334,579
Canada
Revenues from External Customers and Long-Lived Assets [Line Items]
Total Revenues									132,573	126,874	135,527
Total Assets	68,043				68,515				68,043	68,515	68,164
Europe
Revenues from External Customers and Long-Lived Assets [Line Items]
Total Revenues									47,524	42,248	37,787
Total Assets	34,612				38,870				34,612	38,870	35,734
Other Foreign Countries
Revenues from External Customers and Long-Lived Assets [Line Items]
Total Revenues									36,906	39,438	32,069
Total Assets	$ 22,005				$ 23,932				$ 22,005	$ 23,932	$ 21,726