Inventories, Net and Floor Plan Payable - Floor Plan Payable (Details) - CWGS Enterprises, LLC and Subsidiaries - CWGS Enterprises, LLC and Subsidiaries - Line of Credit $ in Millions			9 Months Ended		12 Months Ended
	Jul. 01, 2016 USD ($)	Jun. 30, 2016 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2015 USD ($)	Dec. 31, 2015 USD ($)
Floor Plan Facility
Floor Plan Payable
Interest expense			$ 14.9	$ 9.4
Notes Payable to Banks | Floor Plan Facility
Floor Plan Payable
Maximum borrowing capacity	$ 1,180.0	$ 880.0
Notes Payable to Banks | Floor Plan Facility, floor plan notes
Floor Plan Payable
Amount outstanding			$ 532.5		$ 598.4
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%
Variable rate basis (as a percent)			0.52		0.36
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%
Letter of Credit | Floor Plan Facility, letters of credit
Floor Plan Payable
Amount outstanding			$ 7.3		$ 7.3
Maximum borrowing capacity			$ 15.0