Stockholders' Equity - Dividends (Details) - USD ($) $ / shares in Units, $ in Millions		3 Months Ended	6 Months Ended
Feb. 10, 2020	Jan. 31, 2020	Jan. 31, 2019	Apr. 30, 2020	Apr. 30, 2019
Stockholders' Equity Note [Abstract]
Dividends on common stock	$ 1.5			$ 1.5	$ 1.5
Dividends on common stock (in dollars per share)	$ 0.03	$ 0	$ 0.03

Amount of cash outflow in the form of ordinary dividends to common shareholders of the parent entity.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 15
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3291-108585

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration