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Warehouse Receivables & Warehouse Lines of Credit - Additional Information (Detail)
 9 Months Ended
Sep. 30, 2019
USD ($)
Sep. 30, 2019
USD ($)
Warehouse Receivables And Warehouse Lines Of Credit [Line Items]    
Proceeds from warehouse lines of credit $ 376,700,000  
Advance warehouse funding $ 376,707,000 $ 376,707,000
Warehouse Agreement Borrowings [Member]    
Warehouse Receivables And Warehouse Lines Of Credit [Line Items]    
Period of repayment for warehouse lines of credit   1 month
Lines of credit principal outstanding   $ 2,500,000,000