Commitments and Contingencies - Additional Information (Detail) - USD ($)	3 Months Ended
	Aug. 31, 2019	May 31, 2019
Commitments and Contingencies Disclosure [Line Items]
Environmental remediation expense, period of remediation, years	5 years
Estimated liability costs of remediation	$ 916,000	$ 916,000
Estimated liability, measurement period, years	15 years
Estimated liability costs of remediation, current	$ 100,000
Minimum
Commitments and Contingencies Disclosure [Line Items]
Environmental remediation expense	38,000
Maximum
Commitments and Contingencies Disclosure [Line Items]
Environmental remediation expense	$ 131,000