Inventory Other Inventory Items - Homes under construction not subject to a sale contract (Details) $ in Millions	Dec. 31, 2018 USD ($) homes	Dec. 31, 2017 USD ($) homes
Other Inventory, Gross [Abstract]
Number of Speculative Homes | homes	1,443	1,134
Speculative Homes Carrying Value | $	$ 311.0	$ 242.7