Receivables and Revenue Recognition - Revenue Recognition (Details) - USD ($) $ in Millions	3 Months Ended
Apr. 30, 2019	Apr. 30, 2018
Disaggregation of Revenue [Line Items]
Net sales	$ 1,003.1	$ 1,033.2
Revenue related to merchandise credits and deferred revenue	14.0
Jewelry collections
Disaggregation of Revenue [Line Items]
Net sales	532.3	527.1
Engagement jewelry
Disaggregation of Revenue [Line Items]
Net sales	280.4	296.7
Designer jewelry
Disaggregation of Revenue [Line Items]
Net sales	110.9	128.4
All other
Disaggregation of Revenue [Line Items]
Net sales	$ 79.5	$ 81.0

Amount, including tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value-added and excise.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109196051&loc=SL49130539-203045

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=109196051&loc=SL49130545-203045

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109196051&loc=SL49130543-203045

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