Inventories, net and Notes Payable - Floor Plan, net - Floor Plan Payable (Details) $ in Thousands				6 Months Ended	12 Months Ended
	Jun. 29, 2020 USD ($)	May 12, 2020	Oct. 08, 2019	Jun. 30, 2020 USD ($)	Dec. 31, 2019 USD ($)	May 11, 2020
Floor Plan Facility
Floor Plan Payable
Period for temporary reduction in consolidated current ratio		4 months
Number of days into 2021 the notice can be given		7 days
Maximum borrowing capacity				$ 1,379,750	$ 1,379,750
Quarterly reduction in maximum borrowing capacity				3,000
FLAIR offset account amount				216,900	87,000
FLAIR Maximum Percentage		30.00%				20.00%
Voluntary principal payment	$ 20,000
Floor Plan Facility | London Interbank Offered Rate (LIBOR) | Minimum
Floor Plan Payable
Variable rate spread (as a percent)		2.05%
Floor Plan Facility | London Interbank Offered Rate (LIBOR) | Maximum
Floor Plan Payable
Variable rate spread (as a percent)		3.00%
Floor Plan Facility | Base Rate | Minimum
Floor Plan Payable
Variable rate spread (as a percent)		0.55%
Floor Plan Facility | Base Rate | Maximum
Floor Plan Payable
Variable rate spread (as a percent)		1.50%
Letters of credit | Floor Plan Facility
Floor Plan Payable
Maximum borrowing capacity				15,000
Line of Credit | Floor Plan Facility
Floor Plan Payable
Maximum borrowing capacity				$ 54,000	$ 60,000
Line of Credit | Notes Payable to Banks | Floor Plan Facility, floor plan notes | London Interbank Offered Rate (LIBOR)
Floor Plan Payable
Variable rate spread (as a percent)				2.05%	2.15%
Variable rate basis (as a percent)				0.17	1.71
Line of Credit | Notes Payable to Banks | Floor Plan Facility, floor plan notes | London Interbank Offered Rate (LIBOR) | Minimum
Floor Plan Payable
Variable rate spread (as a percent)			2.05%
Line of Credit | Notes Payable to Banks | Floor Plan Facility, floor plan notes | London Interbank Offered Rate (LIBOR) | Maximum
Floor Plan Payable
Variable rate spread (as a percent)			2.50%
Line of Credit | Notes Payable to Banks | Floor Plan Facility, floor plan notes | Base Rate | Minimum
Floor Plan Payable
Variable rate spread (as a percent)			0.55%
Line of Credit | Notes Payable to Banks | Floor Plan Facility, floor plan notes | Base Rate | Maximum
Floor Plan Payable
Variable rate spread (as a percent)			1.00%