CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Debt Instrument, Convertible, Remaining Discount Amortization Period	3 years 6 months
Current assets:
Cash and cash equivalents	$ 572,358	$ 880,129
Accounts receivable, net	81,478	98,294
Prepaid expenses and other current assets	98,169	94,025
Total current assets	752,005	1,072,448
Property, equipment and software, net	146,897	151,145
Goodwill	327,430	286,989
Intangible assets, net	49,032	19,196
Investments (including $84,861 and $109,751 at September 30, 2018 and December 31, 2017, respectively, at fair value)	109,306	135,189
Other non-current assets	19,250	12,538
Total Assets	1,403,920	1,677,505
Current liabilities:
Accounts payable	16,810	31,968
Accrued merchant and supplier payables	484,626	770,335
Accrued expenses and other current liabilities	269,726	331,196
Total current liabilities	771,162	1,133,499
Convertible senior notes, net	198,575	189,753
Other non-current liabilities	102,543	102,408
Total Liabilities	1,072,280	1,425,660
Commitments and contingencies (see Note 9)
Stockholders' Equity
Common stock, par value $0.0001 per share, 2,010,000,000 shares authorized; 758,800,610 shares issued and 570,198,368 shares outstanding at September 30, 2018; 748,541,862 shares issued and 559,939,620 shares outstanding at December 31, 2017	76	75
Additional paid-in capital	2,222,423	2,174,708
Treasury stock, at cost, 188,602,242 shares at September 30, 2018 and December 31, 2017	(867,450)	(867,450)
Accumulated deficit	(1,056,727)	(1,088,204)
Accumulated other comprehensive income (loss)	32,329	31,844
Total Groupon, Inc. Stockholders' Equity	330,651	250,973
Noncontrolling interests	989	872
Total Equity	331,640	251,845
Total Liabilities and Equity	$ 1,403,920	$ 1,677,505