Geographic Breakdown of Revenues and Total Assets (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Nov. 30, 2014	Nov. 30, 2013	Nov. 30, 2014	Nov. 30, 2013	May 31, 2014
Revenues from External Customers and Long-Lived Assets [Line Items]
Total Revenues	$ 240,619	$ 200,493	$ 428,740	$ 374,804
Total Assets	533,703		533,703		484,941
United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Total Revenues	177,593	137,601	315,657	261,406
Total Assets	400,144		400,144		353,624
Canada
Revenues from External Customers and Long-Lived Assets [Line Items]
Total Revenues	40,042	38,426	72,118	71,354
Total Assets	71,668		71,668		68,515
Europe
Revenues from External Customers and Long-Lived Assets [Line Items]
Total Revenues	13,464	12,198	23,910	20,631
Total Assets	38,574		38,574		38,870
Other Foreign Countries
Revenues from External Customers and Long-Lived Assets [Line Items]
Total Revenues	9,520	12,268	17,055	21,413
Total Assets	$ 23,317		$ 23,317		$ 23,932