Inventories, Net and Floor Plan Payable - Floor Plan Payable (Details) - Line of Credit $ in Millions		6 Months Ended	12 Months Ended
	Jul. 01, 2016 USD ($)	Jun. 30, 2017 USD ($)	Dec. 31, 2016 USD ($)	Jun. 30, 2016 USD ($)
Notes Payable to Banks | Floor Plan Facility
Floor Plan Payable
Maximum borrowing capacity	$ 1,180.0			$ 880.0
Amount outstanding		$ 780.9	$ 625.2
Offset account		$ 86.5	$ 68.5
Notes Payable to Banks | Floor Plan Facility, floor plan notes | London Interbank Offered Rate (LIBOR)
Floor Plan Payable
Variable rate spread (as a percent)		2.15%	2.05%
Variable rate basis (as a percent)		1.05	0.62
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%
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%
Notes Payable to Banks | Floor Plan Facility, floor plan notes | Base Rate | Minimum
Floor Plan Payable
Variable rate spread (as a percent)	0.55%
Notes Payable to Banks | Floor Plan Facility, floor plan notes | Base Rate | Maximum
Floor Plan Payable
Variable rate spread (as a percent)	1.00%
Letters of credit
Floor Plan Payable
Maximum borrowing capacity		$ 15.0