Computation of Earnings Per Share (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Feb. 28, 2014	Feb. 28, 2013	Feb. 28, 2014	Feb. 28, 2013
Denominator:
Denominator for basic earnings per share - weighted average common shares outstanding (including shares issuable for vested restricted stock units)	24,334	23,996	24,320	23,995
Effect of unvested restricted stock units	33	262	29	233
Diluted shares used in per share calculation	24,367	24,257	24,349	24,228
Net income	$ 4,537	$ 5,037	$ 15,815	$ 16,362
Earnings per share:
Basic (in dollars per share)	$ 0.19	$ 0.21	$ 0.65	$ 0.68
Diluted (in dollars per share)	$ 0.19	$ 0.21	$ 0.65	$ 0.68