Summary of Estimated Fair Values of Separately Identifiable Assets Acquired and Liabilities Assumed (Detail) - USD ($) $ in Thousands	Jul. 31, 2017	Apr. 30, 2017	Jul. 31, 2016	Jan. 08, 2016
Business Acquisition [Line Items]
Goodwill	$ 2,344		$ 73,915
Oncura
Business Acquisition [Line Items]
Cash				$ 400
Accounts receivable				300
Inventory				200
Other assets				400
Property, plant, and equipment				400
Goodwill		$ 0		16,400
Intangible assets				4,100
Total assets acquired				22,200
Accounts payable and accrued expenses				(900)
Deferred revenue				(1,100)
Total liabilities assumed				(2,000)
Total purchase price				20,200
Oncura | Trade names
Business Acquisition [Line Items]
Intangible assets				1,000
Oncura | Customer relationships
Business Acquisition [Line Items]
Intangible assets				$ 3,100