Reconciliation of Denominator Used in Computation of Basic and Diluted Earnings per Share (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
Earnings Per Share [Abstract]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount									5,000	3,000	0
Denominator:
Denominator for basic earnings per share—weighted average common shares outstanding (including shares issuable for vested restricted stock units)									24,360,000	24,325,000	24,226,000
Effect of unvested restricted stock units									18,000	32,000	43,000
Diluted shares used in per share calculation									24,378,000	24,357,000	24,269,000
Net income	$ 3,441	$ 2,425	$ 4,795	$ 4,771	$ 4,593	$ 4,537	$ 5,581	$ 5,697	$ 15,432	$ 20,408	$ 22,754
Earnings per share:
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