Selected Quarterly Financial Data (Unaudited) - (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								9 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	Jan. 31, 2018	Apr. 30, 2018	Apr. 30, 2017	Apr. 30, 2016
Selected Quarterly Financial Data (Unaudited)
Net sales					$ 614,977	$ 562,523	$ 591,846	$ 549,800		$ 2,511,469	$ 2,319,146	$ 1,858,182
Gross Profit	$ 635,800	$ 585,508	$ 648,004	$ 642,157	201,035	185,727	193,224	178,585		818,576	758,571	593,164
Net income	$ 205,792	$ 195,420	$ 212,260	$ 205,104	$ 14,273	$ 8,226	$ 17,224	$ 9,163		$ 62,971	$ 48,886	$ 12,564
Weighted average shares outstanding:
Basic (in shares)					40,956	40,943	40,943	38,201		41,015,000	40,260,000	32,799,000
Diluted (in shares)	41,048	41,036	41,006	40,971	41,759	41,578	41,320	38,602		42,163,000	41,070,000	33,125,000
Net income (loss) per share:
Basic (in dollars per share)					$ 0.35	$ 0.20	$ 0.42	$ 0.24		$ 1.54	$ 1.21	$ 0.38
Diluted (in dollars per share)	$ 0.24	$ 0.48	$ 0.44	$ 0.37	$ 0.33	$ 0.20	$ 0.42	$ 0.24		$ 1.49	$ 1.19	$ 0.38
Provisional income tax benefit		$ 7,800								$ 6,700
Decrease from provisional amount		$ 1,100							$ 1,100
Interest rate swap and cap mark-to-market	$ 5,100									$ 6,125	$ 382	$ 19