Noncontrolling Interest (Schedule of Changes in Equity, Including Equity Attributable to Noncontrolling Interests (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
	Jun. 29, 2017	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance				$ 266,056	$ 263,597
Net income (loss)		$ 9,497	$ (4,532)	11,835	(18,703)
Stock based compensation				8,573	9,115
Exercise of options and warrants				76	490
Employee stock purchase plan				1,895	2,299
Foreign currency translation adjustment		(306)	246	(815)	682
Purchase of treasury shares				(801)	(864)
Investments by noncontrolling interests				3,403	3,443
Return of equity to noncontrolling interests	$ (1,000)				(959)
Ending balance		290,222	259,100	290,222	259,100
Comprehensive loss:
Net income (loss)		9,497	(4,532)	11,835	(18,703)
Other comprehensive income (loss):
Foreign currency translation adjustment		(306)	246	(815)	682
Comprehensive income (loss)		9,191	(4,286)	11,020	(18,021)
On Deck Capital, Inc's stockholders' equity
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance				262,045	259,525
Net income (loss)				13,642	(16,630)
Stock based compensation				8,573	9,115
Exercise of options and warrants				76	490
Employee stock purchase plan				1,895	2,299
Foreign currency translation adjustment				(448)	375
Purchase of treasury shares				(801)	(864)
Investments by noncontrolling interests				0	0
Return of equity to noncontrolling interests					0
Ending balance		284,982	254,310	284,982	254,310
Comprehensive loss:
Net income (loss)				13,642	(16,630)
Other comprehensive income (loss):
Foreign currency translation adjustment				(448)	375
Comprehensive income (loss)				13,194	(16,255)
Noncontrolling interest
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance				4,011	4,072
Net income (loss)				(1,807)	(2,073)
Stock based compensation				0	0
Exercise of options and warrants				0	0
Employee stock purchase plan				0	0
Foreign currency translation adjustment				(367)	307
Purchase of treasury shares				0	0
Investments by noncontrolling interests				3,403	3,443
Return of equity to noncontrolling interests					(959)
Ending balance		$ 5,240	$ 4,790	5,240	4,790
Comprehensive loss:
Net income (loss)				(1,807)	(2,073)
Other comprehensive income (loss):
Foreign currency translation adjustment				(367)	307
Comprehensive income (loss)				$ (2,174)	$ (1,766)