Segments - Net Sales, Adjusted EBITDA and Certain Other Measures (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Oct. 31, 2017	Oct. 31, 2016	Oct. 31, 2017	Oct. 31, 2016
Segment information
Net sales	$ 648,004	$ 591,846	$ 1,290,161	$ 1,141,646
Gross profit	212,260	193,224	417,364	371,809
Depreciation and amortization	16,713	17,368	33,058	33,163
Adjusted EBITDA	54,245	49,519	106,994	95,460
Geographic divisions
Segment information
Net sales	641,918	586,628	1,278,285	1,131,633
Gross profit	210,034	191,445	413,059	368,285
Depreciation and amortization	16,466	17,072	32,492	32,579
Adjusted EBITDA	53,651	49,188	105,877	94,796
Other
Segment information
Net sales	6,086	5,218	11,876	10,013
Gross profit	2,226	1,779	4,305	3,524
Depreciation and amortization	60	79	124	159
Adjusted EBITDA	594	331	1,117	664
Corporate
Segment information
Depreciation and amortization	$ 187	$ 217	$ 442	$ 425