Segments - Net Sales, Adjusted EBITDA and Certain Other Measures (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
Segment information
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
Depreciation and Amortization									65,530	69,240	64,215
Adjusted EBITDA									199,258	188,229	138,183
Total assets	1,454,511				1,393,265				1,454,511	1,393,265	1,240,814
Geographic divisions
Segment information
Net sales									2,487,557	2,298,871	1,842,634
Gross Profit									809,884	750,564	587,213
Depreciation and Amortization									64,491	68,001	63,093
Adjusted EBITDA									196,903	186,155	137,459
Total assets	1,434,371				1,376,655				1,434,371	1,376,655	1,217,871
Other.
Segment information
Net sales									23,912	20,275	15,548
Gross Profit									8,692	8,007	5,951
Depreciation and Amortization									242	310	295
Adjusted EBITDA									2,355	2,074	724
Total assets	12,854				11,916				12,854	11,916	12,310
Corporate
Segment information
Depreciation and Amortization									797	929	827
Total assets	$ 7,286				$ 4,694				$ 7,286	$ 4,694	$ 10,633