Debt (Schedule of Line of Credit Facilities) (Details) - USD ($)		3 Months Ended		9 Months Ended		12 Months Ended
		Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Line of Credit Facility [Line Items]
Borrowings outstanding		$ 553,000,000	$ 579,500,000	$ 553,000,000	$ 579,500,000	$ 541,500,000
Agency Credit Facility
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity		300,000,000	300,000,000	300,000,000	300,000,000	300,000,000
Borrowing base		174,548,000	246,448,000	174,548,000	246,448,000	225,642,000
Borrowings outstanding		0	0	0	0	0
Available borrowing capacity	[1]	174,548,000	246,448,000	174,548,000	246,448,000	225,642,000
Average Borrowings Outstanding:		0	0	0	0	0
Borrowing costs - interest	[2]	0	0	0	0	0
Borrowing costs - fee amortization	[2]	640,000	628,000	2,028,000	2,085,000	2,752,000
Total borrowing costs		640,000	628,000	2,028,000	2,085,000	2,752,000
SFS Credit Facility
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity		1,035,000,000	1,035,000,000	1,035,000,000	1,035,000,000	1,035,000,000
Borrowing base		554,969,000	613,952,000	554,969,000	613,952,000	547,586,000
Borrowings outstanding		553,000,000	579,500,000	553,000,000	579,500,000	541,500,000
Available borrowing capacity	[1]	1,969,000	34,452,000	1,969,000	34,452,000	6,086,000
Average Borrowings Outstanding:		523,397,000	589,413,000	527,204,000	534,144,000	541,004,000
Borrowing costs - interest	[3]	3,694,000	3,698,000	10,824,000	10,527,000	14,060,000
Borrowing costs - fee amortization	[3]	739,000	584,000	2,156,000	1,017,000	1,720,000
Total borrowing costs		$ 4,433,000	$ 4,282,000	$ 12,980,000	$ 11,544,000	$ 15,780,000
Weighted-average cost of borrowing (as a percent)		3.40%	2.90%	3.30%	2.90%	2.90%
Total
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity		$ 1,335,000,000	$ 1,335,000,000	$ 1,335,000,000	$ 1,335,000,000
Borrowing base		729,517,000	860,400,000	729,517,000	860,400,000	$ 773,228,000
Borrowings outstanding		553,000,000	579,500,000	553,000,000	579,500,000	541,500,000
Available borrowing capacity	[1]	176,517,000	280,900,000	176,517,000	280,900,000	231,728,000
Average Borrowings Outstanding:		523,397,000	589,413,000	527,204,000	534,144,000	541,004,000
Borrowing costs - interest		3,694,000	3,698,000	10,824,000	10,527,000	14,060,000
Borrowing costs - fee amortization		1,379,000	1,212,000	4,184,000	3,102,000	4,472,000
Total borrowing costs		$ 5,073,000	$ 4,910,000	$ 15,008,000	$ 13,629,000	$ 18,532,000

[1] The available borrowing capacity is calculated as the borrowing base less borrowings outstanding.

[2] Borrowing costs related to the Agency Credit Facility, which include interest and fees, are reflected in the Condensed Consolidated Statements of Operations as Interest Expense. See the table below for additional information related to Interest Expense associated with the Agency Credit Facility.

[3] Borrowing costs related to the SFS Credit Facility are reflected in the Condensed Consolidated Statements of Operations within Cost of Finance Revenues. For the three months ended September 30, 2016, the weighted average cost of borrowings related to the SFS Credit Facility was approximately 3.4%. For the nine months ended September 30, 2016, the weighted average cost of borrowings related to the SFS Credit Facility was approximately 3.3%. For the year ended December 31, 2015 and for the three and nine months ended September 30, 2015, the weighted average cost of borrowings related to the SFS Credit Facility was approximately 2.9%.