REVENUE RECOGNITION - Additional Information (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2018 USD ($) number_of_day
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Cumulative effect of change in accounting principle, net of tax	$ 88,945
Minimum
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Contract with customer, billing cycle | number_of_day	30
Maximum
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Contract with customer, billing cycle | number_of_day	150
Total Groupon, Inc. Stockholders' Equity
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Cumulative effect of change in accounting principle, net of tax	$ 88,945
Total Groupon, Inc. Stockholders' Equity | Accounting Standards Update 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Cumulative effect of change in accounting principle, net of tax	88,900
Cumulative Effect on Retained Earnings, Tax	$ 6,700