Debt (Schedule of Outstanding Debt Amount) (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014		Dec. 31, 2013
Debt Instrument [Line Items]
Balance outstanding	$ 8.8		$ 102.8
Balance outstanding	1,351.3		935.6
Balance outstanding	300.0		350.2
Restricted cash and cash equivalents pledged as collateral	205.4		111.3
Revolving Secured Line of Credit [Member]
Debt Instrument [Line Items]
Balance outstanding	8.8		102.8
Amount available for borrowing	226.2	[1]	132.2	[1]
Interest rate	2.03%		2.04%
Warehouse Facility II [Member]
Debt Instrument [Line Items]
Balance outstanding	0		0
Amount available for borrowing	325.0	[1]	325.0	[1]
Loans pledged as collateral	0		0
Restricted cash and cash equivalents pledged as collateral	2.9		1.2
Interest rate	2.15%		2.17%
Warehouse Facility IV [Member]
Debt Instrument [Line Items]
Balance outstanding	25.0		0
Amount available for borrowing	50.0	[1]	75.0	[1]
Loans pledged as collateral	44.9		0
Restricted cash and cash equivalents pledged as collateral	1.4		0.2
Interest rate	2.15%		2.17%
Warehouse Facility V [Member]
Debt Instrument [Line Items]
Balance outstanding	0
Amount available for borrowing	75.0	[1]	75.0	[1]
Loans pledged as collateral	0
Restricted cash and cash equivalents pledged as collateral	1.3		0.3
Interest rate	1.75%		1.77%
Term ABS 2011-1 [Member]
Debt Instrument [Line Items]
Balance outstanding	0		144.2
Loans pledged as collateral	0		215.3
Restricted cash and cash equivalents pledged as collateral	0		23.2
Interest rate	0.00%		3.01%
Term ABS 2012-1 [Member]
Debt Instrument [Line Items]
Balance outstanding	88.2		201.3
Loans pledged as collateral	169.7		240.4
Restricted cash and cash equivalents pledged as collateral	22.8		23.5
Interest rate	2.61%		2.38%
Term ABS 2012-2 [Member]
Debt Instrument [Line Items]
Balance outstanding	252.0		252.0
Loans pledged as collateral	304.3		303.8
Restricted cash and cash equivalents pledged as collateral	32.0		27.7
Interest rate	1.63%		1.63%
Term ABS 2013-1 [Member]
Debt Instrument [Line Items]
Balance outstanding	140.3		140.3
Loans pledged as collateral	183.7		184.3
Restricted cash and cash equivalents pledged as collateral	17.6		15.3
Interest rate	1.31%		1.31%
Term ABS 2013-2 [Member]
Debt Instrument [Line Items]
Balance outstanding	197.8		197.8
Loans pledged as collateral	244.3		250.5
Restricted cash and cash equivalents pledged as collateral	21.6		18.7
Interest rate	1.67%		1.67%
Term ABS 2014-1 [Member]
Debt Instrument [Line Items]
Balance outstanding	299.0
Loans pledged as collateral	440.5
Restricted cash and cash equivalents pledged as collateral	34.3
Interest rate	1.72%
Term ABS 2014-2 [Member]
Debt Instrument [Line Items]
Balance outstanding	349.0
Loans pledged as collateral	444.9
Restricted cash and cash equivalents pledged as collateral	70.0
Interest rate	2.05%
2017 Senior Notes [Member]
Debt Instrument [Line Items]
Balance outstanding	0	[2]	350.2	[2]
Interest rate	0.00%		9.125%
Unamortized debt premium net			0.2
2021 Senior Notes [Member]
Debt Instrument [Line Items]
Balance outstanding	$ 300.0	[2]	$ 0	[2]
Interest rate	6.125%		0.00%

[1] {F|ahBzfndlYmZpbGluZ3MtaHJkcmoLEgZYTUxEb2MiXlhCUkxEb2NHZW5JbmZvOjBmN2JhNTQ5MDIxZjRiNzY4NDk4OWVhNzNmNTQ1ZmM2fFRleHRTZWxlY3Rpb246RkRCMkNFRjkyQzA1RTgzMThBRENFRjdFNDc4QUNEQTYM}

[2] As of December 31, 2013, the outstanding balance presented for the 2017 Senior Notes includes a net unamortized debt premium of $0.2 million.