SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Derivative Assets and Liabilities (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019
Mortgage Banking Activities
Co-broker fees	$ 8.3	$ 2.9
Fair value of expected guaranty obligation recognized at commitment	$ 1.3	$ 4.1

Decrease in gains from mortgage banking gains due to the recognition at commitment of the fair value of expected guaranty obligations.

No definition available.

Name:	wd_FairValueOfExpectedGuaranteeObligation
Namespace Prefix:	wd_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration