Inventories, net and Notes Payable - Floor Plan, net - Floor Plan Payable (Details) - Line of Credit $ in Millions		12 Months Ended
	Jul. 01, 2016 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014	Jun. 30, 2016 USD ($)
Notes Payable to Banks | Floor Plan Facility
Floor Plan Payable
Maximum borrowing capacity	$ 1,180.0				$ 880.0
Amount outstanding		$ 625.2	$ 598.4
Offset account		$ 68.5	$ 13.6
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%	2.40%	2.10%
Variable rate basis (as a percent)		0.62	0.36	0.16
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