Debt (Schedule of Additional Information Related to Debt Instruments) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Revolving Secured Line of Credit [Member]
Debt Instrument [Line Items]
Maximum outstanding balance	$ 296.6	$ 282.9	$ 296.6	$ 282.9
Average outstanding balance	148.8	81.0	117.0	84.7
Warehouse Facility II [Member]
Debt Instrument [Line Items]
Maximum outstanding balance	201.0	201.0	201.0	201.0
Average outstanding balance	201.0	88.4	110.7	90.7
Warehouse Facility IV [Member]
Debt Instrument [Line Items]
Maximum outstanding balance	0.0	0.0	0.0	100.0
Average outstanding balance	0.0	0.0	0.0	2.2
Warehouse Facility V [Member]
Debt Instrument [Line Items]
Maximum outstanding balance	75.0	0.0	75.0	0.0
Average outstanding balance	50.5	0.0	29.4	0.0
Warehouse Facility VI [Member]
Debt Instrument [Line Items]
Maximum outstanding balance	0.0	0.0	0.0	0.0
Average outstanding balance	0.0	0.0	0.0	0.0
Warehouse Facility VII [Member]
Debt Instrument [Line Items]
Maximum outstanding balance	125.0	25.0	125.0	101.5
Average outstanding balance	100.5	1.9	61.1	2.1
Warehouse Facility VIII [Member]
Debt Instrument [Line Items]
Maximum outstanding balance	149.0	0.0	149.0	0.0
Average outstanding balance	$ 69.9	$ 0.0	$ 38.7	$ 0.0