Derivative and Hedging Instruments (Schedule of Terms of Interest Rate Cap Agreements) (Details) - USD ($) $ in Millions		Jun. 30, 2019		Dec. 31, 2018
Derivative [Line Items]
Interest rate caps, fair value of less than $0.1 million		$ 0.0		$ 0.0
Warehouse Facility II [Member]
Derivative [Line Items]
Debt facility financing amount	[1],[2]	400.0
Warehouse Facility II [Member] | 5.50% Cap Interest Rate [Member]
Derivative [Line Items]
Debt facility financing amount		400.0		400.0
Notional		$ 205.0		$ 205.0
Cap Interest Rate	[3]	5.50%		5.50%
Warehouse Facility IV [Member]
Derivative [Line Items]
Debt facility financing amount		$ 250.0	[1],[2]	$ 250.0
Notional		250.0		250.0
Warehouse Facility IV [Member] | 5.50% Cap Interest Rate [Member]
Derivative [Line Items]
Notional				$ 25.0
Cap Interest Rate	[3]			5.50%
Warehouse Facility IV [Member] | 6.50% Cap Interest Rate [Member]
Derivative [Line Items]
Notional		$ 100.0		$ 75.0
Cap Interest Rate	[3]	6.50%		6.50%
Warehouse Facility IV [Member] | 6.50% Cap Interest Rate Additional [Member]
Derivative [Line Items]
Notional		$ 150.0		$ 150.0
Cap Interest Rate	[3]	6.50%		6.50%
Warehouse Facility V [Member]
Derivative [Line Items]
Debt facility financing amount	[1],[2]	$ 100.0
Warehouse Facility V [Member] | 6.50% Cap Interest Rate [Member]
Derivative [Line Items]
Debt facility financing amount		100.0		$ 100.0
Notional		$ 75.0		$ 75.0
Cap Interest Rate	[3]	6.50%		6.50%
Term ABS 2016-1 [Member] | 5.00% Cap Interest Rate [Member]
Derivative [Line Items]
Debt facility financing amount				$ 125.3
Notional				$ 64.2
Cap Interest Rate	[3]			5.00%
Warehouse Facility VII [Member]
Derivative [Line Items]
Debt facility financing amount	[1],[2]	$ 150.0
Warehouse Facility VII [Member] | 5.50% Cap Interest Rate [Member]
Derivative [Line Items]
Debt facility financing amount		150.0		$ 150.0
Notional		$ 150.0		$ 150.0
Cap Interest Rate	[3]	5.50%		5.50%

[1] Financing made available only to a specified subsidiary of the Company.

[2] Interest rate cap agreements are in place to limit the exposure to increasing interest rates

[3] Rate excludes the spread over the LIBOR rate.