Net Income (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, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Net income (loss)	$ 4,748	$ (1,054)	$ (595)	$ (14,771)
Less: net loss attributable to noncontrolling interest	232	0	232	0
Less: Accretion of dividends on redeemable convertible preferred stock	0	(3,596)	0	(6,200)
Net income (loss) attributable to On Deck Capital, Inc. common stockholders	$ 4,980	$ (4,650)	$ (363)	$ (20,971)
Weighted-average common shares outstanding: Basic	69,479,737	5,262,317	69,366,278	4,983,554
Diluted weighted-average common shares outstanding	75,680,290	5,262,317	69,366,278	4,983,554
Net income (loss) attributable to On Deck Capital, Inc. common stockholders per common share:
Basic (in dollars per share)	$ 0.07	$ (0.88)	$ (0.01)	$ (4.21)
Diluted (in dollars per share)	$ 0.07	$ (0.88)	$ (0.01)	$ (4.21)
Stock Options [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Weighted average effect of dilutive securities	5,819,581	0	0	0
Restricted Stock and RSUs [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Weighted average effect of dilutive securities	40,032	0	0	0
Employee stock purchase program [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Weighted average effect of dilutive securities	58,776	0	0	0
Warrant [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Weighted average effect of dilutive securities	282,164	0	0	0