Segments - Net Sales, Adjusted EBITDA and Certain Other Measures (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jan. 31, 2018	Jan. 31, 2017	Jan. 31, 2018	Jan. 31, 2017
Segment information
Net sales	$ 585,508	$ 562,523	$ 1,875,669	$ 1,704,169
Gross Profit	195,420	185,727	612,784	557,536
Depreciation and Amortization	16,490	18,316	49,548	51,479
Adjusted EBITDA	42,207	40,678	149,201	136,138
Geographic divisions
Segment information
Net sales	579,974	557,774	1,858,259	1,689,407
Gross Profit	193,329	183,503	606,388	551,788
Depreciation and Amortization	16,252	18,018	48,744	50,597
Adjusted EBITDA	41,658	39,910	147,534	134,706
Other.
Segment information
Net sales	5,534	4,749	17,410	14,762
Gross Profit	2,091	2,224	6,396	5,748
Depreciation and Amortization	59	77	183	236
Adjusted EBITDA	549	768	1,667	1,432
Corporate
Segment information
Depreciation and Amortization	$ 179	$ 221	$ 621	$ 646