Acquisitions - Assets (Liabilities) Acquired (Assumed) at Fair Value (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Tangible assets (liabilities) acquired (assumed):
Goodwill	$ 413,123	$ 386,941	$ 359,117
Cash paid for acquisitions, net of cash acquired	47,571	48,418	$ 99,240
2019 Acquisitions
Tangible assets (liabilities) acquired (assumed):
Inventories, net		19,856
Prepaid expenses and other assets		95
Property and equipment, net		359
Accounts payable		(2)
Accrued liabilities		(114)
Total tangible net assets acquired		20,194
Goodwill		28,224
Purchase Price		48,418
Cash paid for acquisitions, net of cash acquired		48,418
Inventory purchases financed via floor plan		(13,854)
Cash payment net of floor plan financing		$ 34,564
2020 Acquisitions
Tangible assets (liabilities) acquired (assumed):
Accounts receivable, net	3,094
Inventories, net	17,211
Prepaid expenses and other assets	643
Property and equipment, net	1,077
Operating lease assets	1,859
Finance lease asset	2,373
Accounts payable	(1,628)
Accrued liabilities	(2,839)
Operating lease liabilities	(1,859)
Finance lease liabilities	(2,373)
Total tangible net assets acquired	17,558
Intangible assets	3,832
Goodwill	26,182
Purchase Price	47,572
Cash paid for acquisitions, net of cash acquired	47,572
Inventory purchases financed via floor plan	(10,350)
Cash payment net of floor plan financing	37,222
2020 Acquisitions | Trademarks and trade names
Tangible assets (liabilities) acquired (assumed):
Intangible assets	725
2020 Acquisitions | Supplier And Customer Relationships [Member]
Tangible assets (liabilities) acquired (assumed):
Intangible assets	$ 3,107