Noncontrolling Interest (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
	Jun. 29, 2017	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance				$ 263,597	$ 329,422
Net income (loss)		$ (4,532)	$ (17,173)	(18,703)	(49,022)
Stock based compensation				9,115	11,399
Exercise of options and warrants				490	168
Employee stock purchase plan				2,299	3,996
Foreign currency translation adjustment		246	210	682	393
Purchase of shares for treasury				(864)	(576)
Investments by noncontrolling interests				3,443
Return of equity to noncontrolling interest	$ (1,000)			(959)
Ending balance		259,100	295,780	259,100	295,780
Comprehensive loss:
Net income (loss)		(4,532)	(17,173)	(18,703)	(49,022)
Other comprehensive income (loss):
Foreign currency translation adjustment		246	210	682	393
Comprehensive loss		(4,286)	(16,963)	(18,021)	(48,629)
On Deck Capital, Inc.'s stockholders' equity
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance				259,525	322,813
Net income (loss)				(16,630)	(47,102)
Stock based compensation				9,115	11,399
Exercise of options and warrants				490	168
Employee stock purchase plan				2,299	3,996
Foreign currency translation adjustment				375	216
Purchase of shares for treasury				(864)	(576)
Investments by noncontrolling interests				0
Return of equity to noncontrolling interest				0
Ending balance		254,310	290,914	254,310	290,914
Comprehensive loss:
Net income (loss)				(16,630)	(47,102)
Other comprehensive income (loss):
Foreign currency translation adjustment				375	216
Comprehensive loss				(16,255)	(46,886)
Noncontrolling interest
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance				4,072	6,609
Net income (loss)				(2,073)	(1,920)
Stock based compensation				0	0
Exercise of options and warrants				0	0
Employee stock purchase plan				0	0
Foreign currency translation adjustment				307	177
Purchase of shares for treasury				0	0
Investments by noncontrolling interests				3,443
Return of equity to noncontrolling interest				(959)
Ending balance		$ 4,790	$ 4,866	4,790	4,866
Comprehensive loss:
Net income (loss)				(2,073)	(1,920)
Other comprehensive income (loss):
Foreign currency translation adjustment				307	177
Comprehensive loss				$ (1,766)	$ (1,743)