Financial Instruments (Narrative) (Details) - USD ($)	3 Months Ended
	Apr. 30, 2019	Apr. 30, 2018	Jan. 31, 2019	Jan. 31, 2018
Investments, All Other Investments [Abstract]
Securities in a continuous unrealized loss position for more than 12 months	$ 0			$ 0
Gain (loss) from sale or redemption of available for sale securities	0	$ 0
Proceeds from sale and maturity of marketable securities	4,600,000	74,800,000
Direct investments in privately held companies	109,800,000		$ 111,600,000
Positive adjustment on certain of its privately held investments	500,000	4,600,000
Other than temporary impairment losses, investments	$ 3,200,000	$ 2,000,000.0