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Related-Party Transactions - Additional Information (Detail) - USD ($)
3 Months Ended 9 Months Ended
Sep. 30, 2015
Sep. 30, 2014
Sep. 30, 2015
Sep. 30, 2014
Affiliates [Member]        
Related Party Transaction [Line Items]        
Real estate inventory acquisitions from affiliates $ 0 $ 9,500,000 $ 16,800,000 $ 40,500,000