Debt (Summary of Additional Information of Credit facilities) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Revolving Secured Line of Credit [Member]
Debt Instrument [Line Items]
Maximum outstanding balance	$ 206.3	$ 204.7
Average outstanding balance	107.9	80.6
Warehouse Facility II [Member]
Debt Instrument [Line Items]
Maximum outstanding balance	190.0	162.6
Average outstanding balance	27.7	58.4
Warehouse Facility IV [Member]
Debt Instrument [Line Items]
Maximum outstanding balance	35.0	26.6
Average outstanding balance	6.4	15.9
Warehouse Facility V [Member]
Debt Instrument [Line Items]
Maximum outstanding balance	75.0	75.0
Average outstanding balance	$ 15.2	$ 8.5