Segments - Reconciliation of Net Income to Adjusted EBITDA (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Apr. 30, 2018	Jan. 31, 2018	Oct. 31, 2017	Jul. 31, 2017	Apr. 30, 2017	Jan. 31, 2017	Oct. 31, 2016	Jul. 31, 2016	Apr. 30, 2018	Apr. 30, 2017	Apr. 30, 2016
Segments
Net income	$ 205,792	$ 195,420	$ 212,260	$ 205,104	$ 14,273	$ 8,226	$ 17,224	$ 9,163	$ 62,971	$ 48,886	$ 12,564
Interest expense									31,395	29,360	37,418
Write-off of debt discount and deferred financing fees									74	7,103
Interest income									(177)	(152)	(928)
Income tax expense (benefit)									20,883	22,654	12,584
Depreciation expense									24,075	25,565	26,667
Amortization expense									41,455	43,675	37,548
Stock appreciation income or (expense)									2,318	148	1,988
Redeemable noncontrolling interests									1,868	3,536	880
Equity-based compensation									1,695	2,534	2,699
Severance and other permitted costs									581	(157)	379
Transaction costs (acquisitions and other)									3,370	2,249	3,751
Gain on sale of assets									(509)	(338)	(645)
Management fee to related party										188	2,250
Effects of fair value adjustments to inventory									324	946	1,009
Change in fair value of financial instruments	$ 5,100								6,125	382	19
Secondary public offering costs									1,525	1,385
Debt transaction costs									1,285	265
Adjusted EBITDA									$ 199,258	$ 188,229	$ 138,183