Revenue Recognition and Contracts with Customers - Schedule of Impact of Adoption of ASU 2014-09 on Revenue Recognized (Detail) - USD ($) $ in Thousands			3 Months Ended	9 Months Ended
Apr. 30, 2019	May 01, 2018	Jan. 31, 2020	Oct. 31, 2019	Jul. 31, 2019	Jan. 31, 2019	Oct. 31, 2018	Jul. 31, 2018	Jan. 31, 2020	Jan. 31, 2019
Disaggregation Of Revenue [Line Items]
Revenue recognized	$ (10,500)	$ (22,600)							$ (31,800)	$ (36,600)
Revenue deferred									26,700	21,000
ASU 2014-09
Disaggregation Of Revenue [Line Items]
Outstanding performance obligations with customers, beginning balance		$ 23,305	$ 5,502	$ 3,114	$ 12,213	$ 8,951	$ 13,621	$ 23,305	12,213	23,305
Revenue recognized			(9,492)	(7,716)	(14,571)	(10,229)	(12,337)	(13,998)
Revenue deferred			11,093	10,104	5,472	9,064	7,667	4,314
Outstanding performance obligations with customers, ending balance	$ 12,213		$ 7,103	$ 5,502	$ 3,114	$ 7,786	$ 8,951	$ 13,621	$ 7,103	$ 7,786