Financial Instruments - Schedule of Gross Unrealized Losses and Fair Values for Investments that were in Continuous Unrealized Loss Position for Less Than 12 Months, Aggregated by Investments Category (Details) $ in Thousands	3 Months Ended	6 Months Ended
	Jul. 31, 2016 USD ($)	Jul. 31, 2016 USD ($)
Schedule Of Available For Sale Securities [Line Items]
Fair Value of Less Than 12 Months	$ 22,183	$ 22,183
Unrealized Losses of Less Than 12 Months	(24)	(24)
Gross realized gains, available-for-sale securities	104	110
U.S. Government Notes
Schedule Of Available For Sale Securities [Line Items]
Fair Value of Less Than 12 Months	2,002	2,002
Unrealized Losses of Less Than 12 Months	(3)	(3)
U.S. Government Agencies
Schedule Of Available For Sale Securities [Line Items]
Fair Value of Less Than 12 Months	6,492	6,492
Unrealized Losses of Less Than 12 Months	(6)	(6)
Corporate Debt Securities
Schedule Of Available For Sale Securities [Line Items]
Fair Value of Less Than 12 Months	13,689	13,689
Unrealized Losses of Less Than 12 Months	$ (15)	$ (15)