Debt (Summary of Additional Information of Credit facilities) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Revolving Secured Line of Credit [Member]
Debt Instrument [Line Items]
Maximum outstanding balance	$ 51.2	$ 201.5	$ 206.3	$ 204.7
Average outstanding balance	6.9	124.6	57.1	102.7
Warehouse Facility II [Member]
Debt Instrument [Line Items]
Maximum outstanding balance	0.0	162.6	190.0	162.6
Average outstanding balance	0.0	56.5	13.8	57.5
Warehouse Facility IV [Member]
Debt Instrument [Line Items]
Maximum outstanding balance	12.0	26.5	35.0	26.6
Average outstanding balance	6.2	24.5	6.3	20.2
Warehouse Facility V [Member]
Debt Instrument [Line Items]
Maximum outstanding balance	29.0	69.1	75.0	75.0
Average outstanding balance	$ 24.3	$ 11.4	$ 19.8	$ 9.9