Commitments and Contingencies (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Loss Contingencies [Line Items]
Lots under Purchase Agreement Recorded	400
Deposits Assets	$ 5.1
Reimbursable Improvement Costs	17.0
Operating Leases, Rent Expense, Net	1.1	$ 1.1	$ 0.9
Letter of Credit [Member]
Loss Contingencies [Line Items]
Maximum borrowing capacity	5.0
Letters of Credit Outstanding, Amount	1.8
Letter of Credit [Member] | Optional Facility Increase [Member]
Loss Contingencies [Line Items]
Maximum borrowing capacity	7.5
Surety Bond [Member]
Loss Contingencies [Line Items]
Outstanding surety bonds	52.1	44.0
Loss Contingency Portion Attributable to Work Remaining to Complete	24.4	15.7
Loans Payable [Member] | Corporate Joint Venture [Member]
Loss Contingencies [Line Items]
Related Party Transaction, Guarantor Obligations, Underlying Asset Class Guaranteed	6.7	8.6
Financial Guarantee [Member] | Corporate Joint Venture [Member]
Loss Contingencies [Line Items]
Long-term Debt, Gross	$ 38.6	$ 56.0