RELATED PARTY TRANSACTIONS WITH IAC - Narrative (Details) - IAC - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Services Agreement
Related Party Transaction [Line Items]
Charges for services rendered pursuant to the services agreement	$ 900,000	$ 1,300,000	$ 3,200,000	$ 3,600,000
Outstanding payables due	0		0		$ 0
Outstanding receivable due	0		0		0
Sublease Agreement
Related Party Transaction [Line Items]
Outstanding payables due	0		0
Outstanding receivable due	0		0		100,000
Revenue from related parties	400,000	500,000	1,200,000	$ 1,400,000
Expenses from related party transactions	300,000		300,000
Tax Sharing Agreement
Related Party Transaction [Line Items]
Outstanding payables due	1,700,000		1,700,000		$ 900,000
Distribution to IAC pursuant to the tax sharing agreement	$ 0	$ 3,100,000	$ 0
Employee Matters Agreement | Class B Common Stock
Related Party Transaction [Line Items]
Issuance of common stock to IAC pursuant to the employee matters agreement (shares)	100,000	100,000	200,000	300,000
Employee Matters Agreement | Class A Common Stock
Related Party Transaction [Line Items]
Issuance of common stock to IAC pursuant to the employee matters agreement (shares)	100,000	0	2,600,000	0