Debt and Financing Arrangements - Note Hedges and Warrants (Details) - USD ($) $ / shares in Units, $ in Thousands, shares in Millions			6 Months Ended
	Feb. 27, 2018	Feb. 23, 2018	Jul. 31, 2018	Jul. 31, 2017	[1]
Debt Instrument [Line Items]
Aggregate amount paid for cost of Note Hedge	$ 80,000
Number of warrants issued, subject to anti-dilution adjustments (in shares)		7.1
Per share value, shares issuable under warrants granted (in dollars per share)		$ 68.06
Proceeds from issuance of warrants related to convertible notes		$ 52,400	$ 52,440	$ 0
Senior Notes | Convertible Senior Notes Due 2023
Debt Instrument [Line Items]
Shares issuable under warrants granted (in shares)		7.1
Conversion price (in dollars per share)		$ 48.36

[1] See Note 2 for a summary of adjustments.