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FINANCIAL INSTRUMENTS AND FAIR VALUE MEASUREMENTS - Narrative (Details)	3 Months Ended	6 Months Ended
	Jun. 30, 2021 USD ($) dealerships swap	Jun. 30, 2021 USD ($) dealerships swap	Dec. 31, 2020 USD ($)	Aug. 31, 2020 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Other deferred costs, net	$ 2,400,000	$ 2,400,000
Amount expected to be reclassified from other comprehensive loss into earnings	(9,800,000)	(9,800,000)
Not Designated as Hedging Instrument
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Notional value	250,000,000.0	250,000,000.0
Accumulated Other Comprehensive Income (Loss) \| Floorplan interest expense
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Tax portion of reclassification out of AOCI		$ 700,000
Accumulated Other Comprehensive Income (Loss) \| Floorplan interest expense \| Not Designated as Hedging Instrument
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Interest Expense	$ 1,000,000.0
Interest Rate Swaps \| Not Designated as Hedging Instrument
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Weighted average interest rate (as a percentage)	1.76%	1.76%
Interest Rate Swaps \| Designated as Hedging Instrument \| Cash Flow Hedging
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Weighted average interest rate (as a percentage)	1.38%	1.38%
Interest Rate Swaps \| Floorplan interest expense \| Not Designated as Hedging Instrument
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Number of additional forward interest rate swaps \| dealerships	5	5
Interest Rate Swaps \| Designated as Hedging Instrument \| Cash Flow Hedging
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Number of additional forward interest rate swaps \| swap	34	34
Notional value	$ 700,400,000	$ 700,400,000
Interest Rate Swaps \| Designated as Hedging Instrument \| Cash Flow Hedging
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Number of additional forward interest rate swaps \| swap	8	8
Notional value	$ 425,000,000.0	$ 425,000,000.0
Weighted average interest rate (as a percentage)	1.20%	1.20%
Senior Notes \| 4.00% Senior Notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Debt issued				$ 550,000,000.0
Interest rate (as a percentage)	4.00%	4.00%
Demand notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Carrying value	$ 100,100,000	$ 100,100,000	$ 60,000,000.0