Percentage points added to the reference rate to compute the variable rate on the debt instrument.

No definition available.

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Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

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-Topic 835
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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

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

- Definition

Date when the debt instrument is scheduled to be fully repaid, in CCYY-MM-DD format.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 10
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Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of the required periodic payments including both interest and principal payments.

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+ Details

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

- 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
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-Subparagraph (b)
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+ Details

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

- Definition

Indebtedness divided by net capital.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	instant

- Definition

The cash outflow during the period from the repayment of aggregate short-term and long-term debt. Excludes payment of capital lease obligations.

+ References

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-Paragraph 15
-Subparagraph (b)
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+ Details

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

- Definition

Asset coverage ratio.

+ References

No definition available.

+ Details

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Namespace Prefix:	wd_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	duration

- Definition

Debt discount percentage.

+ References

No definition available.

+ Details

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

- Definition

Maximum amount of all incremental term loans.

+ References

No definition available.

+ Details

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Namespace Prefix:	wd_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Number of additional term loans.

+ References

No definition available.

+ Details

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Namespace Prefix:	wd_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

The number of financial covenants included in a financial agreement.

+ References

No definition available.

+ Details

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Namespace Prefix:	wd_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_LongtermDebtTypeAxis=wd_TermLoanMember
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Balance Type:
Period Type:

- Details

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Balance Type:
Period Type:

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Balance Type:
Period Type:

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Period Type:

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DEBT - Notes Payable - Terms (Detail) $ in Millions		3 Months Ended		12 Months Ended	24 Months Ended
DEBT - Notes Payable - Terms (Detail) $ in Millions	Nov. 07, 2018 USD ($) loan	Dec. 31, 2019	Sep. 30, 2019	Dec. 31, 2019 USD ($) item	Dec. 31, 2019 USD ($)
Term Loan
Debt
Quarterly equal installments					$ 0.8
Credit Agreement
Debt
Number of financial covenants \| item				1
Credit Agreement \| Minimum
Debt
Asset Coverage Ratio				1.50
Credit Agreement \| Term Loan
Debt
Amount of loan agreement	$ 300.0
Discount on issue of term loan (as a percent)	0.50%
Quarterly equal installments				$ 0.8
Debt instrument maturity date				Nov. 07, 2025
Credit Agreement \| Term Loan \| Minimum
Debt
Number of additional term loans \| loan	1
Credit Agreement \| Term Loan \| Maximum
Debt
Maximum amount of all incremental term loans	$ 150.0
Consolidated Corporate Leverage Ratio		2.00		2.00	2.00
Credit Agreement \| Term Loan \| 30-day LIBOR
Debt
Percentage added to reference rate				2.00%
Term Loan Agreement \| Amendment to Term Loan
Debt
Percentage added to reference rate		2.00%	2.25%
Term Loan Agreement \| Prior Term Loan
Debt
Repayment of previous term loan	$ 165.4
Term Loan Agreement \| Prior Term Loan \| Other operating expense
Debt
Loss on extinguishment of debt				$ 2.1