Fair Value Disclosures (Details Textual) $ in Millions	Jul. 31, 2018 USD ($) investment
Debt Instrument [Line Items]
Investments in an unrealized loss positions (in investments) \| investment	188
Convertible Senior Notes, 1.250% [Member] \| Senior Notes [Member]
Debt Instrument [Line Items]
Long-term debt, fair value \| $	$ 310.5

Number of investment positions in available-for-sale investments in a continuous unrealized loss position for which an other-than-temporary impairment (OTTI) has not been recognized in the income statement.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 6
-Subparagraph (b)(3)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27290-111563

Name:	us-gaap_AvailableforsaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositions1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant