Defined Benefit Pension Plans - Additional Information (Detail) - USD ($)	6 Months Ended
	Oct. 31, 2017	Oct. 31, 2016
Retirement Benefits [Abstract]
Employer contributions	$ 600,000	$ 555,000
Company expected contributions remainder of fiscal year	$ 0
Assumed as expected long-term rate of return	7.75%	8.00%