Warrants (Q3) (Details) - $ / shares	1 Months Ended	9 Months Ended
Dec. 31, 2020	Sep. 30, 2021
Warrants (Details) [Line Items]
Warrant expiration term	5 years	5 years
Sale price (in dollars per share)		$ 10.00
Class A Ordinary Shares [Member] \| Additional Issue of Common Stock or Equity [Member]
Warrants (Details) [Line Items]
Number of trading days	20 days	20 days
Percentage of exercise price of public warrants is adjusted higher than the market value of newly issued price	115.00%	115.00%
Percentage of redemption triggered price is adjusted higher than the market value of newly issued price	180.00%
Class A Ordinary Shares [Member] \| Additional Issue of Common Stock or Equity [Member] \| Minimum [Member]
Warrants (Details) [Line Items]
Sale price (in dollars per share)	$ 9.20	$ 9.20
Percentage of redemption triggered price is adjusted higher than the market value of newly issued price		100.00%
Class A Ordinary Shares [Member] \| Additional Issue of Common Stock or Equity [Member] \| Maximum [Member]
Warrants (Details) [Line Items]
Percentage of aggregate gross proceeds of issuance available for funding of business combination	60.00%	60.00%
Percentage of redemption triggered price is adjusted higher than the market value of newly issued price		180.00%
Redemption of Warrants When Price Exceeds $18.00 [Member] \| Class A Ordinary Shares [Member]
Warrants (Details) [Line Items]
Warrant redemption price (in dollars per unit)	$ 0.01	$ 0.01
Minimum days required to redeem the warrants	30 days	30 days
Number of trading days	30 days	30 days
Number of consecutive trading days	20 days	20 days
Redemption of Warrants When Price Exceeds $18.00 [Member] \| Class A Ordinary Shares [Member] \| Minimum [Member]
Warrants (Details) [Line Items]
Sale price (in dollars per share)	$ 18.00	$ 18.00
Redemption of Warrants When Price Exceeds $10.00 [Member] \| Class A Ordinary Shares [Member]
Warrants (Details) [Line Items]
Warrant redemption price (in dollars per unit)	$ 0.10	$ 0.10
Minimum days required to redeem the warrants	30 days	30 days
Redemption of Warrants When Price Exceeds $10.00 [Member] \| Class A Ordinary Shares [Member] \| Minimum [Member]
Warrants (Details) [Line Items]
Sale price (in dollars per share)	$ 10.00	$ 10.00
Redemption of Warrants When Price Exceeds $10.00 [Member] \| Class A Ordinary Shares [Member] \| Private Placement Warrants [Member] \| Minimum [Member]
Warrants (Details) [Line Items]
Sale price (in dollars per share)	$ 18.00	$ 18.00

Price of a single share of a number of saleable stocks of a company.

No definition available.

Name:	us-gaap_SharePrice
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:perShareItemType
Balance Type:	na
Period Type:	instant

- Definition

Redemption price per share or per unit of warrants or rights outstanding.

+ References

No definition available.

+ Details

Name:	wald_ClassOfWarrantOrRightRedemptionPriceOfWarrantsOrRights
Namespace Prefix:	wald_
Data Type:	dtr-types:perShareItemType
Balance Type:	na
Period Type:	instant

- Definition

Period to provide written notice to redeem warrants, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

Name:	wald_NoticePeriodToRedeemWarrants
Namespace Prefix:	wald_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of trading days for common stock price to exceed threshold, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

Name:	wald_NumberOfTradingDays
Namespace Prefix:	wald_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage of the aggregate gross proceeds from such issuances represent the total equity proceeds, and interest thereon, available for the funding of a Business Combination on the date of the completion of a Business Combination (net of redemptions).

+ References

No definition available.

+ Details

Name:	wald_PercentageOfAggregateGrossProceedsOfIssuanceAvailableForFundingOfBusinessCombination
Namespace Prefix:	wald_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage of the exercise price of the public warrants will be adjusted (to the nearest cent) to be equal to or higher of the market value and the newly issued price.

+ References

No definition available.

+ Details

Name:	wald_PercentageOfExercisePriceOfPublicWarrantsIsAdjustedHigherThanTheMarketValueOfNewlyIssuedPrice
Namespace Prefix:	wald_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage of redemption trigger price will be adjusted (to the nearest cent) to be equal to or higher than the market value and the newly issued price.

+ References

No definition available.

+ Details

Name:	wald_PercentageOfRedemptionTriggeredPriceIsAdjustedHigherThanTheMarketValueOfNewlyIssuedPrice
Namespace Prefix:	wald_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Threshold period of specified trading days that common stock price exceeds threshold price per share, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

Name:	wald_TradingDaysThreshold
Namespace Prefix:	wald_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Warrant expiration term.

+ References

No definition available.

+ Details

Name:	wald_WarrantExpirationTerm
Namespace Prefix:	wald_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- References

No definition available.

+ Details

Name:	wald_WarrantsDetailsLineItems
Namespace Prefix:	wald_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_StatementClassOfStockAxis=us-gaap_CommonClassAMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_SubsidiarySaleOfStockAxis=wald_SecondOfferingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ScheduleOfSharesSubjectToMandatoryRedemptionBySettlementTermsAxis=wald_WarrantsAndRightsSubjectToMandatoryRedemptionOneMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ScheduleOfSharesSubjectToMandatoryRedemptionBySettlementTermsAxis=wald_WarrantsAndRightsSubjectToMandatoryRedemptionTwoMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_SubsidiarySaleOfStockAxis=wald_PrivatePlacementWarrantsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: