Commitments and Contingencies Commitments and Contingencies (Details) $ in Millions	Sep. 30, 2017 USD ($)
Commitments and Contingencies [Abstract]
Letters of credit and completion bonds	$ 167.7
Performance bonds outstanding	118.8
Performance letters of credit outstanding	32.9
Financial letters of credit	8.5
Financial letters of credit representing deposits on land and lot purchase agreements	7.8
Financial Bonds	7.5
Unrecorded conditional purchase obligation	$ 672.9