Financial Instruments - Schedule of Amortized Cost and Estimated Fair Value of Marketable Securities by Contractual Maturity (Details) (Details) $ in Thousands	Jan. 31, 2017 USD ($)
Fair Value Disclosures [Abstract]
Due within one year, Amortized Cost	$ 103,213
Due in one to five years, Amortized Cost	260,335
Total, Amortized Cost	363,548
Due within one year, Fair Value	103,238
Due in one to five years, Fair Value	259,748
Total, Fair Value	$ 362,986