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, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Net income (loss)	$ (17,173)	$ 3,507	$ (49,022)	$ 2,912
Net loss attributable to noncontrolling interests	539	226	1,920	458
Net income (loss) attributable to On Deck Capital, Inc. common stockholders	$ (16,634)	$ 3,733	$ (47,102)	$ 3,370
Weighted-average common shares outstanding:
Basic (in shares)	70,971,895	69,678,742	70,750,037	69,472,636
Weighted-average effect of dilutive securities:
Diluted weighted-average common shares outstanding (in shares)	70,971,895	75,125,740	70,750,037	75,414,348
Net income (loss) attributable to On Deck Capital, Inc. common stockholders per common share:
Basic (USD per share)	$ (0.23)	$ 0.05	$ (0.67)	$ 0.05
Diluted (USD per share)	$ (0.23)	$ 0.05	$ (0.67)	$ 0.04
Stock options
Weighted-average effect of dilutive securities:
Incremental common shares attributable to dilutive effect of share-based payment arrangements (in shares)	0	5,151,449	0	5,607,795
Restricted stock and RSU's
Weighted-average effect of dilutive securities:
Incremental common shares attributable to dilutive effect of share-based payment arrangements (in shares)	0	16,531	0	52,229
Employee stock purchase program
Weighted-average effect of dilutive securities:
Incremental common shares attributable to dilutive effect of share-based payment arrangements (in shares)	0	0	0	0
Warrants to purchase common stock
Weighted-average effect of dilutive securities:
Incremental common shares attributable to dilutive effect of share-based payment arrangements (in shares)	0	279,018	0	281,688