SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Real Estate [Line Items]
Real estate inventory	$ 5,904,196	$ 5,332,426
East
Real Estate [Line Items]
Real estate inventory		$ 13,500
Minimum
Real Estate [Line Items]
Non-refundable deposit percentage of purchase price	15.00%
Maximum
Real Estate [Line Items]
Non-refundable deposit percentage of purchase price	25.00%