Revisions of Prior Period Financial Statements (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Loans and finance receivables	$ 1,227,811		$ 1,227,811				$ 1,169,407
Total assets	1,275,653		1,275,653				1,161,820
Accrued expenses and other liabilities	65,775		65,775				36,708
Total liabilities	942,704		942,704				859,335
Accumulated deficit	(178,313)		(178,313)				(196,959)
Total On Deck Capital, Inc. stockholders' equity	315,264		315,264				297,952
Total stockholders' equity	317,942	$ 288,592	317,942	$ 288,592	$ 317,842	$ 311,596	302,485	$ 276,170	$ 266,113	$ 264,842
Income Statement [Abstract]
Interest and finance income	108,211	99,317	319,651	277,755
Gross revenue	112,550	102,840	332,771	288,436
Net revenue	58,190	52,010	169,456	143,903
Income (loss) from operations, before provision for income taxes	6,510	9,338	17,542	11,374
Net Income (loss)	$ 8,142	9,338	$ 15,638	11,374
Previously Reported
Statement of Financial Position [Abstract]
Loans and finance receivables							1,169,157
Total assets							1,161,570
Accrued expenses and other liabilities							34,654
Total liabilities							857,281
Accumulated deficit							(195,155)
Total On Deck Capital, Inc. stockholders' equity							299,756
Total stockholders' equity							304,289
Income Statement [Abstract]
Interest and finance income		99,476		278,216
Gross revenue		102,999		288,897
Net revenue		52,169		144,364
Income (loss) from operations, before provision for income taxes		9,497		11,835
Net Income (loss)		9,497		11,835
Restatement Adjustment
Statement of Financial Position [Abstract]
Loans and finance receivables							250
Total assets							250
Accrued expenses and other liabilities							2,054
Total liabilities							2,054
Accumulated deficit							(1,804)
Total On Deck Capital, Inc. stockholders' equity							(1,804)
Total stockholders' equity							$ (1,804)
Income Statement [Abstract]
Interest and finance income		(159)		(461)
Gross revenue		(159)		(461)
Net revenue		(159)		(461)
Income (loss) from operations, before provision for income taxes		(159)		(461)
Net Income (loss)		$ (159)		$ (461)