CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - 9 months ended Sep. 30, 2018 - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Treasury Stock	Accumulated Deficit	Accumulated Other Comprehensive Income (Loss)	Total Groupon, Inc. Stockholders' Equity	Non-controlling Interests
Beginning balance (in shares) at Dec. 31, 2017		748,541,862
Beginning balance at Dec. 31, 2017	$ 251,845	$ 75	$ 2,174,708		$ (1,088,204)	$ 31,844	$ 250,973	$ 872
Treasury stock, beginning balance (in shares) at Dec. 31, 2017				(188,602,242)
Treasury stock, beginning balance at Dec. 31, 2017	867,450			$ (867,450)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect of change in accounting principle, net of tax	88,945				88,945		88,945
Reclassification for impact of U.S. tax rate change					(161)	161
Net income (loss) attributable to noncontrolling interest	(47,874)				(57,307)			9,433
Net income (loss) attributable to parent	(57,307)						(57,307)
Foreign currency translation	1,166					1,166	1,166
Unrealized gain (loss) on available-for-sale securities, net of tax	$ (842)					(842)	(842)
Exercise in stock options (in shares)	670,393	670,393
Exercise of stock options	$ 76		76				76
Vesting of restricted stock units and performance share units (in shares)		11,007,259
Vesting of restricted stock units and performance share units		$ 1	(1)
Shares issued under employee stock purchase plan (in shares)		1,621,061
Shares issued under employee stock purchase plan	5,634		5,634				5,634
Shares issued to settle liability-classified awards (in shares)		1,240,379
Shares issued to settle liability-classified awards	6,436		6,436				6,436
Tax withholdings related to net share settlements of stock-based compensation awards (in shares)		(4,280,344)
Tax withholdings related to net share settlements of stock-based compensation awards	(19,030)		(19,030)				(19,030)
Stock-based compensation on equity-classified awards	54,600		54,600				54,600
Distributions to noncontrolling interest holders	(9,316)							(9,316)
Ending balance (in shares) at Sep. 30, 2018		758,800,610
Ending balance at Sep. 30, 2018	331,640	$ 76	$ 2,222,423		$ (1,056,727)	$ 32,329	$ 330,651	$ 989
Treasury stock, ending balance (in shares) at Sep. 30, 2018				(188,602,242)
Treasury stock, ending balance at Sep. 30, 2018	$ 867,450			$ (867,450)