Reconciliation of Changes in Projected Benefit Obligation and Fair Value of Plan Assets and Funded Status for Gerstenslager Plan (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	May 31, 2014	May 31, 2013	May 31, 2012
Change in benefit obligation
Benefit obligation, beginning of year	$ 31,930	$ 33,023
Interest cost	1,403	1,361	1,213
Actuarial loss (gain)	3,002	(1,810)
Benefits paid	(796)	(644)
Benefit obligation, end of year	35,539	31,930	33,023
Change in plan assets
Fair value, beginning of year	24,442	19,746
Actual return on plan assets	2,524	4,355	(789)
Company contributions	300	985
Benefits paid	(796)	(644)
Fair value, end of year	26,470	24,442	19,746
Funded status	(9,069)	(7,488)
Amounts recognized in the consolidated balance sheets consist of:
Other liabilities	(9,069)	(7,488)
Accumulated other comprehensive income	14,028	11,899
Amounts recognized in accumulated other comprehensive income consist of:
Net loss	14,028	11,899
Total	$ 14,028	$ 11,899