Goodwill and Intangible Assets - Definite-Lived Intangible Assets (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Oct. 31, 2017	Apr. 30, 2017
Definite lived intangible assets
Gross carrying amount	$ 315,030	$ 306,606
Accumulated amortization	136,740	115,681
Net carrying value	$ 178,290	$ 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	$ 279,000	$ 273,196
Accumulated amortization	131,012	111,291
Net carrying value	$ 147,988	$ 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	18 years 3 months 18 days
Gross carrying amount	$ 26,250	$ 25,250
Accumulated amortization	2,501	1,718
Net carrying value	$ 23,749	$ 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
Weighted average amortization period	8 years 3 months 18 days	8 years
Gross carrying amount	$ 6,644	$ 5,644
Accumulated amortization	2,553	2,176
Net carrying value	$ 4,091	$ 3,468
Vendor agreement | Minimum
Definite lived intangible assets
Estimated useful lives	8 years
Vendor agreement | Maximum
Definite lived intangible assets
Estimated useful lives	10 years
Leasehold interests
Definite lived intangible assets
Weighted average amortization period	9 years	8 years 2 months 12 days
Gross carrying amount	$ 2,866	$ 2,516
Accumulated amortization	661	496
Net carrying value	$ 2,205	$ 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	15 years	13 years
Non-compete agreements
Definite lived intangible assets
Estimated useful lives	5 years
Weighted average amortization period	5 years
Gross carrying amount	$ 270
Accumulated amortization	13
Net carrying value	$ 257