Debt (Schedule of Additional Information Related to Debt Instruments) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Revolving Secured Line of Credit [Member]
Debt Instrument [Line Items]
Maximum outstanding balance	$ 268.2	$ 276.4
Average outstanding balance	85.2	88.4
Warehouse Facility II [Member]
Debt Instrument [Line Items]
Maximum outstanding balance	201.0	201.0
Average outstanding balance	20.4	93.0
Warehouse Facility IV [Member]
Debt Instrument [Line Items]
Maximum outstanding balance	0.0	100.0
Average outstanding balance	0.0	4.4
Warehouse Facility V [Member]
Debt Instrument [Line Items]
Maximum outstanding balance	50.0	0.0
Average outstanding balance	8.2	0.0
Warehouse Facility VI [Member]
Debt Instrument [Line Items]
Maximum outstanding balance	0.0	101.5
Average outstanding balance	0.0	2.3
Warehouse Facility VII [Member]
Debt Instrument [Line Items]
Maximum outstanding balance	100.0	0.0
Average outstanding balance	21.7	0.0
Warehouse Facility VIII [Member]
Debt Instrument [Line Items]
Maximum outstanding balance	49.0	0.0
Average outstanding balance	$ 7.6	$ 0.0