Debt (Schedule of Additional Information Related to Debt Instruments) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Revolving Secured Line of Credit [Member]
Debt Instrument [Line Items]
Maximum outstanding balance	$ 92.1	$ 142.6	$ 186.4	$ 206.3
Average outstanding balance	13.3	30.0	30.6	48.0
Warehouse Facility II [Member]
Debt Instrument [Line Items]
Maximum outstanding balance	0.0	200.8	200.1	200.8
Average outstanding balance	0.0	4.4	3.7	10.6
Warehouse Facility IV [Member]
Debt Instrument [Line Items]
Maximum outstanding balance	12.0	12.0	12.0	35.0
Average outstanding balance	12.0	12.0	12.0	8.2
Warehouse Facility V [Member]
Debt Instrument [Line Items]
Maximum outstanding balance	0.0	99.2	100.0	99.2
Average outstanding balance	0.0	9.6	1.4	16.4
Warehouse Facility VI [Member]
Debt Instrument [Line Items]
Maximum outstanding balance	0.0	0.0	49.9	0.0
Average outstanding balance	$ 0.0	$ 0.0	$ 4.0	$ 0.0