Financial Instruments Available for Sale Securities Gain/Loss Activity (Details) - USD ($)	3 Months Ended		9 Months Ended
	Oct. 31, 2017	Oct. 31, 2016	Oct. 31, 2017	Oct. 31, 2016	Jan. 31, 2017
Investments, All Other Investments [Abstract]
Securities in a continuous unrealized loss position for more than 12 months	$ 0		$ 0		$ 0
Cost method investments	116,200,000		116,200,000		$ 117,200,000
Other than temporary impairment losses, investments	$ 3,900,000	$ 0	8,000,000.0	$ 300,000
Gain (loss) from sale or redemption of available for sale securities			0	700,000
Proceeds from sale and maturity of marketable securities			$ 729,300,000	$ 1,557,300,000