SIGNIFICANT ACCOUNTING POLICIES - Additional information (Details)					12 Months Ended
	Oct. 01, 2021 USD ($)	Dec. 31, 2019 USD ($)	Oct. 01, 2019 USD ($)	Sep. 30, 2019 segment	Dec. 31, 2021 USD ($) segment	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Jan. 01, 2022 USD ($)	Jan. 01, 2019 USD ($)	Dec. 31, 2018 USD ($)
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Number of reportable segments | segment				1	3
Impairment losses during period related to goodwill	$ 0	$ 0	$ 0
Contingent consideration liability					$ 0
Advertising expense					716,600,000	$ 567,700,000	$ 688,200,000
Liabilities					851,364,000	824,229,000
Assets					1,299,356,000	1,188,990,000
Expected impact to retained earnings due to adoption of ASU 2020-06		402,326,000			447,992,000	364,761,000	402,326,000			$ 346,208,000
Accumulated Deficit
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Expected impact to retained earnings due to adoption of ASU 2020-06		$ (592,654,000)			$ (571,794,000)	$ (640,909,000)	$ (592,654,000)			$ (610,482,000)
Cumulative effect adjustment | Pro Forma | Accumulated Deficit
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Expected impact to retained earnings due to adoption of ASU 2020-06								$ 61,000,000
Cumulative effect adjustment | ASU 2016-02
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Liabilities									$ 8,800,000
Assets									$ 8,800,000
Minimum
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Hosting arrangement, amortization period					1 year
Minimum | Software development
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Software development costs, depreciation period					1 year
Maximum
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Hosting arrangement, amortization period					5 years
Maximum | Software development
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Software development costs, depreciation period					5 years