Commitments and Contingencies Commitments and Contingencies (Details) $ in Millions	Mar. 31, 2018 USD ($)
Commitments and Contingencies [Abstract]
Letters of credit and completion bonds	$ 179.9
Performance bonds outstanding	121.0
Performance letters of credit outstanding	43.5
Financial letters of credit	7.7
Financial letters of credit representing deposits on land and lot purchase agreements	7.0
Financial Bonds	7.7
Unrecorded conditional purchase obligation	$ 757.7