Quarterly Financial Data (Detail) - USD ($) $ / shares in Units, $ 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
Schedule Of Quarterly Financial Information [Line Items]
Total revenues		$ 60,413	$ 56,342	$ 59,703	$ 61,871	$ 61,077	$ 62,016	$ 57,876	$ 60,168	$ 238,329	$ 241,137	$ 248,731
Gross Profit	[1]	20,580	18,356	20,825	22,480	22,877	21,579	23,138	23,465	82,241	91,059
Income Before Taxes		5,646	3,746	7,696	7,562	7,368	7,291	8,999	8,868	24,650	32,526	37,113
Net income		$ 3,441	$ 2,425	$ 4,795	$ 4,771	$ 4,593	$ 4,537	$ 5,581	$ 5,697	$ 15,432	$ 20,408	$ 22,754
Basic, in dollars per share		$ 0.14	$ 0.10	$ 0.20	$ 0.20	$ 0.19	$ 0.19	$ 0.23	$ 0.23	$ 0.63	$ 0.84	$ 0.94
Diluted, in dollars per share		$ 0.14	$ 0.10	$ 0.20	$ 0.20	$ 0.19	$ 0.19	$ 0.23	$ 0.23	$ 0.63	$ 0.84	$ 0.94

[1] Gross profit is calculated as total revenues less depreciation of rental and lease equipment, costs of rentals and leases and costs of sales of equipment and other revenues.