DESCRIPTION OF BUSINESS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details) $ in Millions		3 Months Ended
	Dec. 11, 2023 USD ($) collisionCenter	Mar. 31, 2024 USD ($) franchise VehicleBrands segment dealership CollisionRepairCenters states shares	Mar. 31, 2023 USD ($) shares	May 25, 2023 USD ($)
Business Organization [Line Items]
Number of franchises (in franchises) | franchise		206
Number of dealership locations (in dealership locations) | dealership		157
Number of vehicle brands (in vehicle brands) | VehicleBrands		31
Number of collision repair centers (in collision repair centers) | CollisionRepairCenters		37
Number of states (in states) | states		15
Number of reportable segments | segment		2
Retirement of common stock (in shares) | shares		239,790	110,323
Treasury stock, retired (in shares) | shares		239,790	164,527
Cash paid to acquire treasury stock		$ 50.0	$ 20.7
Stock repurchase program, authorized amount				$ 250.0
Stock repurchase program, remaining authorized repurchase amount		$ 152.6
Jim Koons Dealerships
Business Organization [Line Items]
Aggregate purchase price	$ 1,500.0
Assets held for sale	$ 100.9
Number of new vehicle dealerships acquired | collisionCenter	20
Number of collision centers acquired (in collision repair centers) | collisionCenter	6
Jim Koons Dealerships | New vehicle floor plan facility
Business Organization [Line Items]
Aggregate purchase price	$ 256.1
Restricted Share Units
Business Organization [Line Items]
Antidilutive securities excluded from computation of earnings per share | shares		2,877	4,005
Performance share units
Business Organization [Line Items]
Antidilutive securities excluded from computation of earnings per share | shares		14	476
Luxury Brands
Business Organization [Line Items]
Weighted brand mix (percent)		29.00%
Mid-line Import Brands
Business Organization [Line Items]
Weighted brand mix (percent)		41.00%
Domestic Brands
Business Organization [Line Items]
Weighted brand mix (percent)		30.00%