Debt (Narrative) (Details) - USD ($)																				1 Months Ended		12 Months Ended
	Feb. 08, 2019	Jan. 31, 2019	Jan. 28, 2019	Dec. 17, 2018	Aug. 08, 2018	Apr. 17, 2018	Apr. 13, 2018	May 25, 2017	May 24, 2017	May 04, 2017	May 03, 2017	Mar. 20, 2017	Feb. 14, 2017	Dec. 08, 2016	Aug. 19, 2016	Jun. 17, 2016	May 17, 2016	Apr. 28, 2016	Apr. 27, 2016	Jan. 31, 2019	Apr. 30, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Mar. 01, 2019	Feb. 13, 2017	Nov. 30, 2016	Nov. 29, 2016	Jun. 16, 2016	Feb. 26, 2016	Feb. 25, 2016
Debt Instrument [Line Items]
Amount of debt repaid																						$ 632,744,000	$ 273,679,000	$ 398,682,000
Loans held for investment that are pledged as collateral																						$ 1,000,000,000	$ 852,300,000
ODAST II Series 2018-1 | Secured Debt
Debt Instrument [Line Items]
Debt instrument, face amount																					$ 225,000,000
Amount of debt repaid						$ 225,000,000											$ 250,000,000
ODAST II Series 2016-1 | Secured Debt
Debt Instrument [Line Items]
Amount of debt repaid																					$ 250,000,000
Credit Facility Due December 2019 | Revolving Credit Facility
Debt Instrument [Line Items]
Increase in line of credit				$ 19,700,000
RAOD | Revolving Credit Facility
Debt Instrument [Line Items]
Increase in line of credit				$ 100,000,000
Line of credit																														$ 100,000,000	$ 50,000,000
RAOD | Revolving Credit Facility | ODAC | LIBOR
Debt Instrument [Line Items]
Variable interest spread				2.45%				3.00%	2.50%
ODAC | Revolving Credit Facility
Debt Instrument [Line Items]
Borrowing base											75.00%							75.00%	70.00%
ODAC | Revolving Credit Facility | ODAC
Debt Instrument [Line Items]
Line of credit											$ 75,000,000							$ 75,000,000	$ 50,000,000
ODAC | Revolving Credit Facility | ODAC | LIBOR
Debt Instrument [Line Items]
Variable interest spread																		9.25%	8.25%
ODAC | Revolving Credit Facility | ODAC | LIBOR | Minimum
Debt Instrument [Line Items]
Variable interest spread											0.00%
ODAC | Revolving Credit Facility | ODAC | LIBOR | Maximum
Debt Instrument [Line Items]
Variable interest spread											9.25%
Amended ODAC Agreement Due May 2019 | Revolving Credit Facility
Debt Instrument [Line Items]
Borrowing base										85.00%
Amended ODAC Agreement Due May 2019 | Revolving Credit Facility | ODAC
Debt Instrument [Line Items]
Line of credit										$ 100,000,000
Amended ODAC Agreement Due May 2019 | Revolving Credit Facility | ODAC | LIBOR | Minimum
Debt Instrument [Line Items]
Variable interest spread										0.75%
Amended ODAC Agreement Due May 2019 | Revolving Credit Facility | ODAC | LIBOR | Maximum
Debt Instrument [Line Items]
Variable interest spread										7.25%
ODAST II Agreement - Class A | Secured Debt
Debt Instrument [Line Items]
Amount of debt repaid																	$ 211,500,000
Interest rate																	4.21%
ODAST II Agreement - Class B | Secured Debt
Debt Instrument [Line Items]
Amount of debt repaid																	$ 38,500,000
Interest rate																	7.63%
ODAST Agreement | Secured Debt
Debt Instrument [Line Items]
Amount of debt repaid																	$ 175,000,000
ODAST II Agreement Due April 2022 - Class A | Secured Debt
Debt Instrument [Line Items]
Amount of debt repaid						$ 177,500,000
Interest rate						3.50%
ODAST II Agreement Due April 2022 - Class B | Secured Debt
Debt Instrument [Line Items]
Amount of debt repaid						$ 15,500,000
Interest rate						4.02%
ODAST II Agreement Due April 2022 - Class C | Secured Debt
Debt Instrument [Line Items]
Amount of debt repaid						$ 20,000,000
Interest rate						4.52%
ODAST II Agreement Due April 2022 - Class D | Secured Debt
Debt Instrument [Line Items]
Amount of debt repaid						$ 12,000,000
Interest rate						5.85%
ODART | Revolving Credit Facility
Debt Instrument [Line Items]
Increase in line of credit																$ 12,400,000
Line of credit												$ 214,100,000				$ 162,400,000.0													$ 150,000,000
Borrowing base																92.00%
ODART | Revolving Credit Facility | LIBOR
Debt Instrument [Line Items]
Variable interest spread																8.00%
ODART Agreement - Class A | Revolving Credit Facility
Debt Instrument [Line Items]
Increase in line of credit												$ 50,000,000
Borrowing base												85.00%
ODART Agreement - Class B | Revolving Credit Facility
Debt Instrument [Line Items]
Increase in line of credit												$ 1,800,000
Borrowing base												91.00%
ODAF | Secured Debt
Debt Instrument [Line Items]
Line of credit													$ 150,000,000													$ 100,000,000
Line of credit facility, extension in expiration period													6 months
ODAF | Revolving Credit Facility
Debt Instrument [Line Items]
Line of credit															$ 100,000,000
ODAF | Revolving Credit Facility | LIBOR
Debt Instrument [Line Items]
Variable interest spread															7.25%
Borrowing base															80.00%
Debt Facility, Loan Assets of OnDeck, LLC, Due August 2022 | Revolving Credit Facility
Debt Instrument [Line Items]
Line of credit					$ 175,000,000
Variable interest spread					3.00%
Borrowing base					87.50%
PORT II | Revolving Credit Facility
Debt Instrument [Line Items]
Line of credit														$ 200,000,000
Borrowing base														83.00%
PORT II | Revolving Credit Facility | Class A
Debt Instrument [Line Items]
Line of credit														$ 125,000,000
Line of credit, additional funding														$ 75,000,000
PORT II | Revolving Credit Facility | Prime Rate
Debt Instrument [Line Items]
Variable interest spread														2.25%
Debt Facility, Loan Assets of OnDeck, LLC, Due April 2022 | Revolving Credit Facility | Loan Assets of OnDeck, LLC,
Debt Instrument [Line Items]
Line of credit							$ 100,000,000
Variable interest spread							2.00%
Borrowing base							84.50%
Corporate Debt | Revolving Credit Facility
Debt Instrument [Line Items]
Line of credit																											$ 30,000,000	$ 20,000,000
Subsequent Event | ODAST II Series 2018-1 | Revolving Credit Facility
Debt Instrument [Line Items]
Amount of debt repaid																				$ 30,000,000
Subsequent Event | Debt Facility, Sun Trust Facility Agreement, Due January 2021 | Revolving Credit Facility
Debt Instrument [Line Items]
Line of credit		$ 85,000,000	$ 85,000,000																	$ 85,000,000
Subsequent Event | Debt Facility, Sun Trust Facility Agreement, Due January 2021 | Revolving Credit Facility | LIBOR
Debt Instrument [Line Items]
Variable interest spread		3.00%	3.00%
Subsequent Event | ODART Agreement - Class B | Revolving Credit Facility
Debt Instrument [Line Items]
Line of credit																									$ 14,100,000
Subsequent Event | Debt Facility, Loan Assets of OnDeck, LLC, Due April 2022 | Revolving Credit Facility
Debt Instrument [Line Items]
Increase in line of credit	$ 50,000,000
Variable interest spread	0.25%
Subsequent Event | Debt Facility, Loan Assets of OnDeck, LLC, Due April 2022 | Revolving Credit Facility | Loan Assets of OnDeck, LLC,
Debt Instrument [Line Items]
Increase in line of credit	$ 50,000,000
Variable interest spread	0.25%