Revenue Recognition, Contracts with Customers, Remaining Performance Obligations, Assets Recognized for the Costs to Obtain or Fulfill a Contract (Details) - USD ($) $ in Thousands		3 Months Ended
		Jul. 31, 2018	Jul. 31, 2017
Remaining Performance Obligations [Abstract]
Remaining performance obligation		$ 407,200
Assets Recognized for the Costs to Obtain or Fulfill a Contract [Abstract]
Costs capitalized		5,700
Amortization		800
Cost of revenue [Abstract]
Operating and administrative expenses	[1]	253,773	$ 245,738
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2018-08-01
Remaining Performance Obligations [Abstract]
Remaining performance obligation		$ 392,300
Expected timing of satisfaction, period		12 months
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-08-01
Remaining Performance Obligations [Abstract]
Remaining performance obligation		$ 14,900
Expected timing of satisfaction, period
Shipping and Handling [Member]
Cost of revenue [Abstract]
Operating and administrative expenses		$ 7,900	$ 7,800

[1] Due to the retrospective adoption of ASU 2017-07, total net benefits of $1.9 million related to defined benefit and other post-employment benefit plans were reclassified from Operating and Administrative Expenses to Interest and Other Income for the three months ended July 31, 2017. Total net benefits were $2.4 million for the three months ended July 31, 2018. Refer to Note 2, "Recent Accounting Standards," in the Notes to Condensed Consolidated Financial Statements for more information.