Business Acquisitions and Dispositions - Revenues and Other Activities Associated with Disposed Dealerships That Remain in Continuing Operations (Details) - Disposed dealerships that remain in continuing operations - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Income (loss) from operations	$ (1,119)	$ 337	$ (1,964)	$ (2,499)
Gain (loss) on disposal	3,388	(823)	2,273	45,570
Lease exit accrual adjustments and charges	0	0	0	169
Pre-tax income (loss)	2,269	(486)	309	43,240
Total revenues	$ 11,050	$ 110,274	$ 44,817	$ 358,788