Revenue (Details) - USD ($) $ in Millions	3 Months Ended							9 Months Ended		12 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 29, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2019	Dec. 31, 2017
Revenue from External Customer [Line Items]
Contract with Customer, Liability	$ 2.5							$ 0.0		$ 2.5
Revenues	$ 236.3	$ 88.2	$ 65.3	$ 38.5	$ 32.2	$ 23.6	$ 22.6	78.3	$ 83.5	428.3	$ 114.3
Other Revenue (Expense) from Real Estate Operations								0.7		2.3	2.8
Real Estate | Residential Real Estate [Member]
Revenue from External Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax								72.0		351.7	83.9
Land [Member] | Residential Real Estate [Member]
Revenue from External Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax								3.6		55.8	14.6
Land [Member] | Commercial Real Estate [Member]
Revenue from External Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax								$ 2.0		$ 18.5	$ 13.0