Revenues and Total Assets in United States and Other Countries (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	May 31, 2014	Feb. 28, 2014	Nov. 30, 2013	Aug. 31, 2013	May 31, 2013	Feb. 28, 2013	Nov. 30, 2012	Aug. 31, 2012	May 31, 2014	May 31, 2013	May 31, 2012
Revenues from External Customers and Long-Lived Assets [Line Items]
Total Revenues	$ 211,487	$ 163,236	$ 200,493	$ 174,311	$ 201,196	$ 150,975	$ 200,648	$ 161,492	$ 749,527	$ 714,311	$ 623,740
Total Assets	484,941				460,203				484,941	460,203	403,788
United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Total Revenues									540,967	508,928	438,413
Total Assets	353,624				334,579				353,624	334,579	296,240
Canada
Revenues from External Customers and Long-Lived Assets [Line Items]
Total Revenues									126,874	135,527	121,865
Total Assets	68,515				68,164				68,515	68,164	60,334
Europe
Revenues from External Customers and Long-Lived Assets [Line Items]
Total Revenues									42,248	37,787	36,448
Total Assets	38,870				35,734				38,870	35,734	30,352
Other Foreign Countries
Revenues from External Customers and Long-Lived Assets [Line Items]
Total Revenues									39,438	32,069	27,014
Total Assets	$ 23,932				$ 21,726				$ 23,932	$ 21,726	$ 16,862