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Acquisition-related Intangible Assets, Net - Schedule of Acquired Assets (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jul. 31, 2019	Jul. 31, 2018	Jul. 31, 2019	Jul. 31, 2018	Jan. 31, 2019
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	$ 402,400		$ 402,400		$ 398,800
Less accumulated amortization	(124,447)		(124,447)		(85,560)
Total	277,953		277,953		313,240
Goodwill, acquired during period	9,000
Amortization of intangible assets	20,000	$ 5,000	39,000	$ 10,000
Developed technology
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	190,400		190,400		186,800
Finite-lived intangible assets acquired	4,000
Customer relationships
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	189,000		189,000		189,000
Trade name
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	12,000		12,000		12,000
Backlog
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	$ 11,000		$ 11,000		$ 11,000