Segment Results - Schedule of Operating Segment Information (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Segment Reporting Information, Profit (Loss) [Abstract]
Total operating revenue	$ 77.8	$ 89.1	$ 232.5	$ 327.6
Gain (loss) on disposal of commercial real estate properties, net	0.0	0.0	0.5	0.0
Interest expense	(7.1)	(8.2)	(22.7)	(25.4)
Income (loss) from continuing operations before income taxes	3.2	(50.8)	4.9	(43.7)
Commercial Real Estate
Segment Reporting Information, Profit (Loss) [Abstract]
Commercial real estate	35.7	42.7	113.1	118.6
Land Operations
Segment Reporting Information, Profit (Loss) [Abstract]
Revenues	7.7	8.5	29.0	82.4
Materials & Construction
Segment Reporting Information, Profit (Loss) [Abstract]
Revenues	34.4	37.9	90.4	126.6
Operating Segments
Segment Reporting Information, Profit (Loss) [Abstract]
Total operating revenue	77.8	89.1	232.5	327.6
Total operating profit (loss)	15.7	(37.1)	40.9	(0.2)
Gain (loss) on disposal of commercial real estate properties, net	0.0	0.0	0.5	0.0
Interest expense	(7.1)	(8.2)	(22.7)	(25.4)
Operating Segments | Commercial Real Estate
Segment Reporting Information, Profit (Loss) [Abstract]
Commercial real estate	35.7	42.7	113.1	118.6
Total operating profit (loss)	11.0	18.0	37.9	50.6
Operating Segments | Land Operations
Segment Reporting Information, Profit (Loss) [Abstract]
Revenues	7.7	8.5	29.0	82.4
Total operating profit (loss)	3.4	2.8	13.1	15.9
Operating Segments | Materials & Construction
Segment Reporting Information, Profit (Loss) [Abstract]
Revenues	34.4	37.9	90.4	126.6
Total operating profit (loss)	1.3	(57.9)	(10.1)	(66.7)
Other
Segment Reporting Information, Profit (Loss) [Abstract]
Corporate and other expense	$ (5.4)	$ (5.5)	$ (13.8)	$ (18.1)