Percentage of voting equity interests acquired at the acquisition date in the business combination.

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=79982066&loc=d3e1392-128463

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- Definition

In a business combination achieved in stages, this element represents the amount of gain recognized by the entity as a result of remeasuring to fair value the equity interest in the acquiree it held before the business combination.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (g)(2)
-URI http://asc.fasb.org/extlink&oid=79982066&loc=d3e1392-128463

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Balance Type:	credit
Period Type:	duration

- Definition

The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=114001798&loc=d3e33918-111571

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Balance Type:	na
Period Type:	instant

- Definition

Difference between the fair value of payments made and the carrying amount of debt which is extinguished prior to maturity.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 50
-Section 40
-Paragraph 4
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-Name Accounting Standards Codification
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-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3602-108585

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- Definition

The expense recorded to reduce the value of oil and gas assets consisting of proved properties and unproved properties as the estimate of future successful production from these properties is reduced.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
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-Publisher FASB
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-Topic 230
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-Section 45
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-Publisher FASB
-Name Accounting Standards Codification
-Topic 932
-SubTopic 360
-Section 35
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=66906256&loc=d3e66150-109466

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Gain on reduction of contingent consideration liabilities.

+ References

No definition available.

+ Details

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Namespace Prefix:	y_
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- Definition

Investments.

+ References

No definition available.

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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	dei_LegalEntityAxis=y_StrandedOilResourcesCorporationMember
Namespace Prefix:
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Period Type:

- Details

Name:	dei_LegalEntityAxis=y_PrecisionCuttingTechnologiesIncMember
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Amounts of Gross Realized Capital Gains and Gross Realized Capital Losses (Parenthetical) (Detail) - USD ($) $ in Millions		3 Months Ended	6 Months Ended
	Apr. 01, 2020	Jun. 30, 2020	Jun. 30, 2020	Mar. 31, 2020
Investments [Line Items]
Realized loss on early redemption of debt			$ 7.1
Stranded Oil Resources Corporation
Investments [Line Items]
Write-down of oil field assets		$ 44.5	74.4
Precision Cutting Technologies, Inc
Investments [Line Items]
Realized gain on reduction of contingent consideration liabilities			5.0
Wilbert Funeral Services, Inc
Investments [Line Items]
Gain on remeasurement of pre-existing equity ownership to estimated fair value	$ 16.3	$ 16.3	$ 16.3
Equity interest percentage acquired	55.00%
Equity interest percentage				45.00%