FANNIE MAE COMMITMENTS AND PLEDGED SECURITIES - Commitments (Detail) - DUS Risk-Sharing Obligations - Fannie Mae $ in Millions	9 Months Ended
Sep. 30, 2019 USD ($)
LITIGATION, COMMITMENTS, AND CONTINGENCIES
Period of funding for collateral requirement	48 months
Amount of additional capital required to be funded over the next 48 months	$ 66.9
Net worth	689.4
Minimum liquid assets to be maintained to meet operational liquidity requirements	37.8
Operational liquidity	228.5
Minimum
LITIGATION, COMMITMENTS, AND CONTINGENCIES
Net worth requirement	$ 191.4
New Tier 2 loans
LITIGATION, COMMITMENTS, AND CONTINGENCIES
Collateral requirements percentage (as a percent)	0.75%
Period of funding for collateral requirement	48 months
New Tier 2 loans \| Money Market Funds
LITIGATION, COMMITMENTS, AND CONTINGENCIES
Restricted liquidity collateral reduction percentage	5.00%
New Tier 2 loans \| Agency Mortgage Backed Securities
LITIGATION, COMMITMENTS, AND CONTINGENCIES
Restricted liquidity collateral reduction percentage	4.00%

Amount of net capital of broker-dealer.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher SEC
-Name Rule 15c3-1
-Number 240
-Section 15c3-1

+ Details

Name:	srt_NetCapital
Namespace Prefix:	srt_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_LossContingenciesLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The amount of additional collateral required for the lender risk-sharing portfolio over a specified period.

+ References

No definition available.

+ Details

Name:	wd_AdditionalCollateralRequirementOfLenderOverSpecifiedPeriod
Namespace Prefix:	wd_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The percentage of collateral requirements for the lender risk-sharing portfolio.

+ References

No definition available.

+ Details

Name:	wd_CollateralRequirementsPercentage
Namespace Prefix:	wd_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The minimum liquid assets required to be maintained by the entity to meet operational liquidity requirements as of the balance sheet date.

+ References

No definition available.

+ Details

Name:	wd_MinimumLiquidAssetsRequiredToMeetOperationalLiquidityRequirements
Namespace Prefix:	wd_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Represents the net worth (total assets minus total liabilities) required to be maintained by the entity.

+ References

No definition available.

+ Details

Name:	wd_NetWorthRequirement
Namespace Prefix:	wd_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The operational liquidity of the entity as of the balance sheet date.

+ References

No definition available.

+ Details

Name:	wd_OperationalLiquidity
Namespace Prefix:	wd_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The period over which the collateral requirement for loans will be funded.

+ References

No definition available.

+ Details

Name:	wd_PeriodForFundingCollateralRequirement
Namespace Prefix:	wd_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

The percentage of the restricted liquidity collateral haircut.

+ References

No definition available.

+ Details

Name:	wd_RestrictedLiquidityCollateralHaircutPercentage
Namespace Prefix:	wd_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_LossContingenciesByNatureOfContingencyAxis=wd_RiskSharingObligationsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LineOfCreditFacilityAxis=wd_FannieMaeMember
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:	us-gaap_FinancialInstrumentAxis=wd_TierTwoMortgageLoansNewMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsAxis=us-gaap_MoneyMarketFundsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsAxis=us-gaap_MortgageBackedSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: