Derivative and Hedging Instruments (Schedule of Terms of Interest Rate Cap Agreements) (Details) - USD ($)		Sep. 30, 2017	Dec. 31, 2016
Derivative [Line Items]
Debt facility financing amount		$ 3,020,200,000	$ 2,622,100,000
Interest rate caps, fair value of less than $0.1 million		0	0
Warehouse Facility II [Member]
Derivative [Line Items]
Debt facility financing amount	[1],[2]	400,000,000
Warehouse Facility II [Member] | 5.50% Cap Interest Rate [Member]
Derivative [Line Items]
Debt facility financing amount		400,000,000	400,000,000
Notional		$ 325,000,000	$ 325,000,000
Cap Interest Rate	[3]	5.50%	5.50%
Warehouse Facility IV [Member]
Derivative [Line Items]
Debt facility financing amount	[1],[2]	$ 100,000,000
Warehouse Facility IV [Member] | 5.50% Cap Interest Rate Original [Member]
Derivative [Line Items]
Notional		$ 75,000,000	$ 18,800,000
Cap Interest Rate	[3]	5.50%	5.50%
Warehouse Facility IV [Member] | Additional Interest Rate Cap [Member]
Derivative [Line Items]
Notional		$ 25,000,000	$ 56,200,000
Cap Interest Rate	[3]	6.50%	5.50%
Warehouse Facility IV [Member] | 5.50% Cap Interest Rate [Member]
Derivative [Line Items]
Debt facility financing amount		$ 100,000,000	$ 75,000,000
Notional		100,000,000	75,000,000
Warehouse Facility V [Member]
Derivative [Line Items]
Debt facility financing amount	[1],[2]	100,000,000
Warehouse Facility V [Member] | 5.50% Cap Interest Rate [Member]
Derivative [Line Items]
Debt facility financing amount		100,000,000	100,000,000
Notional		$ 75,000,000	$ 75,000,000
Cap Interest Rate	[3]	5.50%	5.50%
Term ABS 2016-1 [Member]
Derivative [Line Items]
Debt facility financing amount	[1],[2]	$ 385,000,000
Term ABS 2016-1 [Member] | 5.00% Cap Interest Rate [Member]
Derivative [Line Items]
Debt facility financing amount		385,000,000.0	$ 385,000,000
Notional		$ 385,000,000	$ 385,000,000
Cap Interest Rate	[3]	5.00%	5.00%

[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.