Financial Instruments (Narrative) (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jul. 31, 2019	Jul. 31, 2018	Jul. 31, 2019	Jul. 31, 2018	Jan. 31, 2019
Investments, All Other Investments [Abstract]
Securities in a continuous unrealized loss position for more than 12 months	$ 0		$ 0		$ 0
Gain (loss) from sale or redemption of available for sale securities			0	$ 0
Proceeds from sale and maturity of marketable securities	22,800,000	$ 71,800,000	27,400,000	146,600,000
Direct investments in privately held companies	121,900,000		121,900,000		$ 111,600,000
Positive adjustment on certain of its privately held investments			1,700,000	6,200,000
Cumulative adjustment on certain of its privately held investments	7,900,000		7,900,000
Other than temporary impairment losses, investments			3,400,000	$ 4,800,000
Cumulative impairments and negative adjustments on certain of its privately held investments	$ 8,200,000		$ 8,200,000