Net Loss Per Common Share (Basic and Diluted Net Loss per Common Share) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Earnings Per Share [Abstract]
Net income (loss)	$ (11,602)	$ (13,141)
Less: net loss attributable to noncontrolling interest	544	568
Net loss attributable to On Deck Capital, Inc. common stockholders	$ (11,058)	$ (12,573)
Weighted-average common shares outstanding, basic and diluted (in shares)	71,854,287	70,366,877
Net loss per common share, basic and diluted (in dollars per share)	$ (0.15)	$ (0.18)