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, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Net income (loss)	$ (18,708)	$ 4,748	$ (31,849)	$ (595)
Less: net loss attributable to noncontrolling interest	813	232	1,381	232
Net income (loss) attributable to On Deck Capital, Inc. common stockholders	$ (17,895)	$ 4,980	$ (30,468)	$ (363)
Weighted-average common shares outstanding:
Basic (in shares)	70,712,142	69,479,737	70,588,784	69,366,278
Weighted-average effect of dilutive securities:
Diluted weighted-average common shares outstanding (in shares)	70,712,142	75,680,290	70,588,784	69,366,278
Net income (loss) attributable to On Deck Capital, Inc. common stockholders per common share:
Basic (USD per share)	$ (0.25)	$ 0.07	$ (0.43)	$ (0.01)
Diluted (USD per share)	$ (0.25)	$ 0.07	$ (0.43)	$ (0.01)
Stock options
Weighted-average effect of dilutive securities:
Incremental common shares attributable to dilutive effect of share-based payment arrangements (in shares)	0	5,819,581	0	0
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	40,032	0	0
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	58,776	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	282,164	0	0