Goodwill and Intangible Assets - Definite-Lived Intangible Assets (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Jul. 31, 2017	Apr. 30, 2017
Definite lived intangible assets
Gross carrying amount	$ 306,606	$ 306,606
Accumulated amortization	126,036	115,681
Net carrying value	$ 180,570	$ 190,925
Customer relationships
Definite lived intangible assets
Weighted average amortization period	10 years 10 months 24 days	10 years 10 months 24 days
Gross carrying amount	$ 273,196	$ 273,196
Accumulated amortization	121,011	111,291
Net carrying value	$ 152,185	$ 161,905
Customer relationships | Minimum
Definite lived intangible assets
Estimated useful lives	5 years	5 years
Customer relationships | Maximum
Definite lived intangible assets
Estimated useful lives	13 years	13 years
Tradenames
Definite lived intangible assets
Weighted average amortization period	18 years 3 months 18 days	18 years 3 months 18 days
Gross carrying amount	$ 25,250	$ 25,250
Accumulated amortization	2,097	1,718
Net carrying value	$ 23,153	$ 23,532
Tradenames | Minimum
Definite lived intangible assets
Estimated useful lives	5 years	5 years
Tradenames | Maximum
Definite lived intangible assets
Estimated useful lives	20 years	20 years
Vendor agreement
Definite lived intangible assets
Estimated useful lives	8 years	8 years
Gross carrying amount	$ 5,644	$ 5,644
Accumulated amortization	2,352	2,176
Net carrying value	$ 3,292	$ 3,468
Leasehold interests
Definite lived intangible assets
Weighted average amortization period	8 years 2 months 12 days	8 years 2 months 12 days
Gross carrying amount	$ 2,516	$ 2,516
Accumulated amortization	576	496
Net carrying value	$ 1,940	$ 2,020
Leasehold interests | Minimum
Definite lived intangible assets
Estimated useful lives	7 years	7 years
Leasehold interests | Maximum
Definite lived intangible assets
Estimated useful lives	13 years	13 years