Reconciliation of Changes in Projected Benefit Obligation and Fair Value of Plan Assets and Funded Status for Gerstenslager Plan (Detail) - USD ($) $ in Thousands	12 Months Ended
	May 31, 2016	May 31, 2015	May 31, 2014
Change in benefit obligation
Benefit obligation, beginning of year	$ 40,227	$ 35,539
Interest cost	1,621	1,541	$ 1,403
Actuarial loss	759	3,924
Benefits paid	(1,439)	(777)
Benefit obligation, end of year	41,168	40,227	35,539
Change in plan assets
Fair value, beginning of year	28,159	26,470
Actual return (loss) on plan assets	(1,154)	1,846	2,524
Company contributions		620
Benefits paid	(1,439)	(777)
Fair value, end of year	25,566	28,159	$ 26,470
Funded status	(15,602)	(12,068)
Amounts recognized in the consolidated balance sheets consist of:
Other liabilities	(15,602)	(12,068)
Amounts recognized in accumulated other comprehensive loss consist of:
Net loss	21,324	17,900
Other Postretirement Benefit Plan
Amounts recognized in the consolidated balance sheets consist of:
Accumulated other comprehensive loss	21,324	17,900
Amounts recognized in accumulated other comprehensive loss consist of:
Total	$ 21,324	$ 17,900