Financial Instruments - Narrative (Detail) - USD ($)	12 Months Ended
	Jan. 31, 2020	Jan. 31, 2019	Jan. 31, 2018
Investments, All Other Investments [Abstract]
Securities in continuous unrealized loss position for greater than twelve months	$ 0	$ 0
Available-for-sale securities gross gains (losses)	0	(1,300,000)	$ (300,000)
Proceeds from sale and maturity of marketable securities	27,400,000	531,000,000.0	1,080,000,000.00
Non-marketable equity securities investments without readily determinable fair value	122,500,000	111,600,000
Positive adjustment on privately held investments	3,200,000	6,200,000
Cumulative adjustment on certain of its privately held investments	9,400,000
Other than temporary impairment losses, investments	4,200,000	$ 4,800,000	$ 15,500,000
Cumulative impairments and negative adjustments on certain of its privately held investments	$ 9,000,000.0