Long-Term Debt - Asset-Based Lending Facility (Details) - USD ($)	12 Months Ended
	Apr. 30, 2017	Apr. 30, 2016	Apr. 30, 2015	Apr. 01, 2014
Long-term debt
Accrued interest payable	$ 721,000	$ 678,000
Deferred financing costs related to credit facility	2,950,000	2,544,000
ABL Facility
Long-term debt
Maximum amount under the facility	300,000,000	200,000,000		$ 200,000,000
Available borrowings under the facility	231,249,000	187,185,000
Borrowings outstanding		101,910,000
Accrued interest payable	532,000	422,000
Interest and other fees paid on the facility	$ 4,148,000	1,900,000	$ 941,000
Maximum amount under the facility, including permitted increases				$ 345,000,000
Accordion feature		$ 100,000,000
Applicable rate of interest during period (as a percent)	2.58%	2.97%
ABL Facility | Swing-line
Long-term debt
Maximum amount under the facility	$ 30,000,000	$ 20,000,000
ABL Facility | Long-term debt, less current portion
Long-term debt
Borrowings outstanding	103,353,000
ABL Facility | Other assets
Long-term debt
Deferred financing costs related to credit facility	2,950,000	$ 2,544,000
ABL Second Amendment
Long-term debt
Maximum amount under the facility	$ 345,000,000
Reduction to interest rate margin at each pricing level (as a percent)	0.25%
ABL Second Amendment | Swing-line
Long-term debt
Maximum amount under the facility	$ 34,500,000