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REVENUE RECOGNITION - Narrative (Details) - USD ($)
$ in Millions
3 Months Ended 6 Months Ended
Jun. 30, 2021
Jun. 30, 2020
Jun. 30, 2021
Jun. 30, 2020
Dec. 31, 2020
Revenue from Contract with Customer [Abstract]          
Deferred revenue $ 5.8   $ 5.8   $ 11.2
Amortization of deferred contract costs 2.6 $ 4.0 5.2 $ 8.7  
Variable consideration from unredeemed vouchers sold in prior periods $ 10.2   $ 13.0