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Segment Information - Text (Detail)
$ in Millions
3 Months Ended 9 Months Ended 12 Months Ended
Sep. 30, 2019
USD ($)
Jun. 30, 2019
USD ($)
Mar. 31, 2019
USD ($)
Dec. 31, 2018
USD ($)
segment
Sep. 29, 2018
USD ($)
Jun. 30, 2018
USD ($)
Mar. 31, 2018
USD ($)
Sep. 30, 2018
USD ($)
Sep. 30, 2017
USD ($)
Sep. 30, 2019
USD ($)
Dec. 31, 2017
USD ($)
Segment Reporting Information [Line Items]                      
Asset impairments               $ 0.3   $ 1.3 $ 47.2
Gain of sale of assets               27.8 $ 113.4 $ 3.0 113.4
Number of business segments | segment       1              
Document Period End Date                   Sep. 30, 2019  
Revenues $ 236.3 $ 88.2 $ 65.3 $ 38.5 $ 32.2 $ 23.6 $ 22.6 78.3 $ 83.5 $ 428.3 114.3
Other Segments [Member]                      
Segment Reporting Information [Line Items]                      
Asset impairments                     $ 5.8
D.R. Horton, Inc. [Member]                      
Segment Reporting Information [Line Items]                      
Revenues                   $ 326.6  
Other Segments [Member] | Disposal Group, Disposed of by Sale, Not Discontinued Operations                      
Segment Reporting Information [Line Items]                      
Gain of sale of assets               9.2      
Purchase price of properties sold               10.5      
FMF Littleton [Member]                      
Segment Reporting Information [Line Items]                      
Gain of sale of assets               $ 14.6