Revenue and Contract Balances (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Disaggregation of Revenue [Line Items]
Total operating revenue	$ 73.9	$ 109.1	$ 154.7	$ 238.5
Commercial Real Estate
Disaggregation of Revenue [Line Items]
Commercial Real Estate	34.0	39.1	77.4	75.9
Land Operations
Disaggregation of Revenue [Line Items]
Revenues	9.8	24.9	21.3	73.9
Land Operations | Development sales revenue
Disaggregation of Revenue [Line Items]
Revenues	2.3	18.1	5.9	30.4
Land Operations | Unimproved/other property sales revenue
Disaggregation of Revenue [Line Items]
Revenues	1.6	0.4	3.7	30.9
Land Operations | Other operating revenue
Disaggregation of Revenue [Line Items]
Revenues	5.9	6.4	11.7	12.6
Materials & Construction
Disaggregation of Revenue [Line Items]
Revenues	$ 30.1	$ 45.1	$ 56.0	$ 88.7