Segments - Reconciliation of Net Income to Adjusted EBITDA (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jan. 31, 2018	Jan. 31, 2017	Jan. 31, 2018	Jan. 31, 2017
Segments
Adjusted EBITDA	$ 42,207	$ 40,678	$ 149,201	$ 136,138
Interest expense	(7,871)	(7,431)	(23,288)	(22,162)
Write-off of debt discount and deferred financing fees		(211)	(74)	(7,103)
Interest income	44	23	93	101
Income tax benefit (expense)	4,488	(5,363)	(15,555)	(12,232)
Depreciation expense	(6,009)	(6,465)	(18,021)	(19,395)
Amortization expense	(10,481)	(11,851)	(31,527)	(32,084)
Stock appreciation (expense) or income	(631)	498	(1,863)	734
Redeemable noncontrolling interests	(340)	(256)	(1,370)	(3,079)
Equity-based compensation	(430)	(622)	(1,277)	(1,981)
Severance and other permitted costs	(8)	(57)	(325)	(315)
Transaction costs (acquisitions and other)	(75)	(305)	(321)	(2,783)
Gain on sale of assets	51	114	648	244
Management fee to related party				(188)
Effects of fair value adjustments to inventory	(89)	(155)	(276)	(776)
Interest rate cap mark-to-market	(276)	(109)	(710)	(241)
Secondary public offering costs	(894)		(1,525)
Debt transaction costs		(261)	(758)	(264)
Net income	$ 19,686	$ 8,227	$ 53,052	$ 34,614