Acquisitions - Additional Information (Detail) - USD ($)				12 Months Ended
	Jan. 09, 2015	Dec. 11, 2014	May 05, 2014	Apr. 30, 2016	Apr. 30, 2015	Apr. 30, 2014	Nov. 25, 2014
Business Acquisition [Line Items]
Goodwill deductible for tax purpose				$ 12,000,000
DRP Acquisition
Business Acquisition [Line Items]
Payments to acquire business, excluding working capital adjustment			$ 22,800,000
Working capital adjustment			1,000,000
Payments to acquire business, net of cash acquired			$ 23,800,000
Business combination, acquisition-related costs					$ 440,000	$ 471,000
Goodwill amortization period for tax purpose				15 years
Battenfeld Acquisition Company Inc
Business Acquisition [Line Items]
Payments to acquire business, excluding working capital adjustment		$ 130,500,000
Working capital adjustment		3,100,000
Payments to acquire business, net of cash acquired					135,437,000
Acquisition payment made through line of credit		100,000,000
Battenfeld Acquisition Company Inc | Amended Unsecured Revolving Credit Facility
Business Acquisition [Line Items]
Line of credit facility, maximum borrowing capacity							$ 125,000,000
B T I Acquisitions Excluding Hooyman LLC
Business Acquisition [Line Items]
Payments to acquire business, net of cash acquired		$ 133,600,000
Hooyman LLC
Business Acquisition [Line Items]
Payments to acquire business, net of cash acquired	$ 1,900,000
BTI Acquisitions
Business Acquisition [Line Items]
Payments to acquire business, net of cash acquired				$ 135,500,000
Business combination, acquisition-related costs					$ 1,700,000