Net Loss Per Common Share (Basic and Diluted Net Loss per Common Share) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Numerator:
Net income (loss)	$ (4,532)	$ (17,173)	$ (18,703)	$ (49,022)
Less: net loss attributable to noncontrolling interest	458	539	2,073	1,920
Net loss attributable to On Deck Capital, Inc. common stockholders	$ (4,074)	$ (16,634)	$ (16,630)	$ (47,102)
Denominator:
Weighted-average common shares outstanding, basic and diluted (in shares)	73,272,085	70,971,895	72,613,221	70,750,037
Net loss per common share, basic and diluted (in dollars per share)	$ (0.06)	$ (0.23)	$ (0.23)	$ (0.67)