Commitments and Contingencies Commitments and Contingencies (Details) $ in Millions	Sep. 30, 2018 USD ($)
Commitments and Contingencies [Abstract]
Letters of credit and completion bonds	$ 205.9
Performance bonds outstanding	150.3
Performance letters of credit outstanding	38.2
Financial letters of credit	10.6
Financial letters of credit representing deposits on land and lot purchase agreements	10.1
Financial Bonds	6.8
Unrecorded conditional purchase obligation	$ 699.9