Income Taxes - Deferred Income Taxes (Details) - USD ($) $ in Thousands	Apr. 30, 2018	Apr. 30, 2017
Deferred income tax assets:
Allowances on accounts and notes receivable	$ 3,540	$ 5,792
Accrued payroll and related costs	1,138	1,651
Insurance reserves	1,734	1,139
Inventory costs	2,013	2,430
Deferred compensation	6,662	9,293
Equity compensation	2,361	3,424
Derivative instrument	561	1,488
Acquisition related costs	1,955	1,732
Net operating loss carry-forwards	1,965	2,949
Deferred rent	488	996
Noncompete agreements	681	819
Other deferred tax assets, net	946	2,576
Total deferred income tax assets	24,044	34,289
Less: Valuation allowance	(448)	(297)
Total deferred income tax assets, net of valuation allowance	23,596	33,992
Deferred income tax liabilities, net
Amortization of intangible assets	(28,641)	(53,345)
Rebates	(253)	(1,007)
Depreciation	(3,596)	(3,808)
Deferred financing costs	(1,848)	(2,652)
Total deferred income tax liabilities	(34,338)	(60,812)
Deferred income tax liabilities, net	$ (10,742)	$ (26,820)