Net Loss Per Common Share (Basic and Diluted Net Loss per Common Share) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Numerator:
Net income (loss)	$ (2,569)	$ (18,708)	$ (14,171)	$ (31,849)
Less: net loss attributable to noncontrolling interest	1,071	813	1,615	1,381
Net loss attributable to On Deck Capital, Inc. common stockholders	$ (1,498)	$ (17,895)	$ (12,556)	$ (30,468)
Denominator:
Weighted-average common shares outstanding, basic and diluted (in shares)	72,688,815	70,712,142	72,276,734	70,588,784
Net loss per common share, basic and diluted (in dollars per share)	$ (0.02)	$ (0.25)	$ (0.17)	$ (0.43)