Goodwill and Intangible Assets - Definite-Lived Intangible Assets (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Jan. 31, 2018	Apr. 30, 2017
Definite-lived intangible assets
Gross Carrying Amount	$ 318,120	$ 306,606
Accumulated Amortization	147,273	115,681
Net Carrying Value	$ 170,847	$ 190,925
Customer relationships
Definite-lived intangible assets
Weighted Average Amortization Period (in years)	10 years 10 months 24 days	10 years 10 months 24 days
Gross Carrying Amount	$ 281,839	$ 273,196
Accumulated Amortization	140,825	111,291
Net Carrying Value	$ 141,014	$ 161,905
Customer relationships | Minimum
Definite-lived intangible assets
Estimated Useful Lives (years)	5 years	5 years
Customer relationships | Maximum
Definite-lived intangible assets
Estimated Useful Lives (years)	13 years	13 years
Tradenames
Definite-lived intangible assets
Weighted Average Amortization Period (in years)	18 years	18 years 3 months 18 days
Gross Carrying Amount	$ 26,250	$ 25,250
Accumulated Amortization	2,901	1,718
Net Carrying Value	$ 23,349	$ 23,532
Tradenames | Minimum
Definite-lived intangible assets
Estimated Useful Lives (years)	5 years	5 years
Tradenames | Maximum
Definite-lived intangible assets
Estimated Useful Lives (years)	20 years	20 years
Vendor agreements
Definite-lived intangible assets
Estimated Useful Lives (years)		8 years
Weighted Average Amortization Period (in years)	8 years 3 months 18 days	8 years
Gross Carrying Amount	$ 6,644	$ 5,644
Accumulated Amortization	2,754	2,176
Net Carrying Value	$ 3,890	$ 3,468
Vendor agreements | Minimum
Definite-lived intangible assets
Estimated Useful Lives (years)	8 years
Vendor agreements | Maximum
Definite-lived intangible assets
Estimated Useful Lives (years)	10 years
Leasehold interests
Definite-lived intangible assets
Weighted Average Amortization Period (in years)	9 years	8 years 2 months 12 days
Gross Carrying Amount	$ 2,866	$ 2,516
Accumulated Amortization	746	496
Net Carrying Value	$ 2,120	$ 2,020
Leasehold interests | Minimum
Definite-lived intangible assets
Estimated Useful Lives (years)	7 years	7 years
Leasehold interests | Maximum
Definite-lived intangible assets
Estimated Useful Lives (years)	15 years	13 years
Other
Definite-lived intangible assets
Estimated Useful Lives (years)	5 years
Weighted Average Amortization Period (in years)	5 years
Gross Carrying Amount	$ 521
Accumulated Amortization	47
Net Carrying Value	$ 474