Segments - Net Sales, Adjusted EBITDA and Certain Other Measures (Details) - USD ($) $ in Thousands	3 Months Ended
	Jul. 31, 2017	Jul. 31, 2016
Segment information
Net sales	$ 642,157	$ 549,800
Gross profit	205,104	178,585
Depreciation and amortization	16,345	15,795
Adjusted EBITDA	52,752	45,941
Geographic divisions
Segment information
Net sales	636,367	545,005
Gross profit	203,024	176,840
Depreciation and amortization	16,026	15,507
Adjusted EBITDA	52,227	45,608
Other
Segment information
Net sales	5,790	4,795
Gross profit	2,080	1,745
Depreciation and amortization	64	80
Adjusted EBITDA	525	333
Corporate
Segment information
Depreciation and amortization	$ 255	$ 208