Debt (Narrative) (Details)					12 Months Ended
		Mar. 30, 2015 USD ($)	Feb. 21, 2014 USD ($)	Jan. 22, 2014 USD ($)	Dec. 31, 2017 USD ($) facility		Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Sep. 30, 2016
Debt Instrument [Line Items]
Maximum hedging reserve					$ 1,000,000
Debt financing amount					$ 3,093,000,000		$ 2,622,100,000
Percentage of collections on contributed loans					6.00%
Monthly servicing fee per financing					6.00%
Debt covenants					$ 1
Proceeds from issuance of senior notes					$ 0		0	$ 248,200,000
Revolving Secured Line Of Credit [Member]
Debt Instrument [Line Items]
Debt maturity date					Jun. 22, 2020
Line of credit facility	[1]				$ 350,000,000
Percentage of net book value of loans					80.00%
Debt financing amount	[2]				$ 13,900,000		0
Revolving Secured Line of Credit Future Maximum Borrowing Capacity [Member]
Debt Instrument [Line Items]
Line of credit facility					$ 315,000,000
Warehouse Facilities [Member]
Debt Instrument [Line Items]
Percentage of net book value of loans					80.00%
Number of warehouse facilities | facility					5
Debt financing amount					$ 825,000,000
Warehouse Facility II [Member]
Debt Instrument [Line Items]
Debt maturity date	[3],[4]				Dec. 20, 2020
Debt financing amount					$ 400,000,000	[3],[5]	$ 400,000,000
Interest rate					0.00%		0.00%
Warehouse Facility IV [Member]
Debt Instrument [Line Items]
Debt maturity date	[3],[4]				Apr. 30, 2020
Debt financing amount					$ 100,000,000	[3],[5]	$ 75,000,000
Interest rate					0.00%		2.77%
Warehouse Facility V [Member]
Debt Instrument [Line Items]
Debt maturity date	[3],[6]				Aug. 18, 2019
Debt financing amount					$ 100,000,000	[3],[5]	$ 100,000,000
Interest rate					0.00%		0.00%
Warehouse Facility VI [Member]
Debt Instrument [Line Items]
Debt maturity date	[3],[4]				Sep. 30, 2020
Debt financing amount	[3]				$ 75,000,000
Interest rate					0.00%		0.00%
2017 Senior Notes [Member]
Debt Instrument [Line Items]
Senior notes stated interest rate									9.125%
Debt Instrument, Repurchase Date			Feb. 21, 2014
Repayments of senior notes			$ 350,000,000
Loss on extinguishment of debt			$ 21,800,000
2021 Senior Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Issuance Date				Jan. 22, 2014
Debt maturity date				Feb. 15, 2021	Feb. 15, 2021
Debt financing amount				$ 300,000,000	$ 300,000,000
Senior notes stated interest rate				6.125%
Interest rate					6.125%		6.125%
2023 Senior Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Issuance Date		Mar. 30, 2015
Debt maturity date		Mar. 15, 2023			Mar. 15, 2023
Debt financing amount		$ 250,000,000			$ 250,000,000
Senior notes stated interest rate		7.375%
Redemption price, percentage of principal amount redeemed		99.266%
Proceeds from issuance of senior notes		$ 248,200,000
Interest rate		7.50%			7.375%		7.375%
London Interbank Offered Rate (LIBOR) [Member] | Revolving Secured Line Of Credit [Member]
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate					1.875%
London Interbank Offered Rate (LIBOR) [Member] | Warehouse Facility II [Member]
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate					1.75%
London Interbank Offered Rate (LIBOR) [Member] | Warehouse Facility IV [Member]
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate					2.25%
London Interbank Offered Rate (LIBOR) [Member] | Warehouse Facility V [Member]
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate					2.25%
London Interbank Offered Rate (LIBOR) [Member] | Warehouse Facility VI [Member]
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate					2.00%
Prime Rate [Member] | Revolving Secured Line Of Credit [Member]
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate					0.875%

[1] The amount of the facility will decrease to $315.0 million on June 22, 2019.

[2] Excludes deferred debt issuance costs of $2.8 million and $2.4 million as of December 31, 2017 and December 31, 2016, respectively, which are included in other assets.

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

[4] Represents the revolving maturity date. The outstanding balance will amortize after the revolving maturity date based on the cash flows of the pledged assets.

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

[6] Represents the revolving maturity date. The outstanding balance will amortize after the revolving maturity date and any amounts remaining on August 18, 2021 will be due on that date.