Financial Instruments (Narrative) (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jul. 31, 2020	Jul. 31, 2019	Jul. 31, 2020	Jul. 31, 2019	Jan. 31, 2020
Debt Securities, Available-for-sale [Line Items]
Securities in a continuous unrealized loss position for more than 12 months	$ 0		$ 0		$ 0
Allowance for credit loss	0		0
Securities, writeoff			0
Gain (loss) from sale or redemption of available for sale securities			0	$ 0
Proceeds from sale and maturity of marketable securities	11,000,000	$ 22,800,000	11,000,000.0	$ 27,400,000
Direct investments in privately held companies	136,200,000		136,200,000		$ 122,500,000
Level 3 | Privately Held
Debt Securities, Available-for-sale [Line Items]
Debt securities, available-for-sale	5,300,000		5,300,000
Amortized c non-marketable debt securities	$ 5,300,000		$ 5,300,000