Employee Pension Plans - Reconciliation of Changes in Projected Benefit Obligation and Fair Value of Plan Assets and Funded Status of Gerstenslager Plan (Detail) - USD ($) $ in Thousands	12 Months Ended
	May 31, 2018	May 31, 2017	May 31, 2016
Change in benefit obligation
Benefit obligation, beginning of year	$ 39,174	$ 41,168
Interest cost	1,522	1,527	$ 1,621
Actuarial gain	(1,516)	(2,459)
Benefits paid	(1,170)	(1,062)
Benefits obligation, end of year	38,010	39,174	41,168
Change in plan assets
Fair value, beginning of year	27,022	25,566
Actuarial return on plan assets	1,361	2,224	(1,154)
Company contributions		294
Benefits paid	(1,171)	(1,062)
Fair value, end of year	27,212	27,022	$ 25,566
Funded status	(10,798)	(12,152)
Amounts recognized in accumulated other comprehensive loss consist of:
Net loss	16,343	17,839
Other Liabilities
Amounts recognized in the consolidated balance sheets consist of:
Amounts recognized in the consolidated balance sheets	(10,798)	(12,152)
Amounts recognized in accumulated other comprehensive loss consist of:
Total	(10,798)	(12,152)
Accumulated Other Comprehensive Loss
Amounts recognized in the consolidated balance sheets consist of:
Amounts recognized in the consolidated balance sheets	16,343	17,839
Amounts recognized in accumulated other comprehensive loss consist of:
Total	$ 16,343	$ 17,839