Derivative Instruments and Risk Management Activities - Impact of Interest Rate Derivative Instruments (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Derivative [Line Items]
Amount of unrealized income (loss), net of tax, recognized in other comprehensive (loss) income	$ (4,238)	$ 7,892
Amount of income (loss) reclassified from other comprehensive (loss) income into statements of operations	346
Amount of income (loss) reclassified from other comprehensive (loss) income into statements of operations		(1,513)
Floorplan interest expense, net
Derivative [Line Items]
Amount of income (loss) reclassified from other comprehensive (loss) income into statements of operations	344
Amount of income (loss) reclassified from other comprehensive (loss) income into statements of operations		(1,737)
Other interest expense, net
Derivative [Line Items]
Amount of income (loss) reclassified from other comprehensive (loss) income into statements of operations	110
Amount of income (loss) reclassified from other comprehensive (loss) income into statements of operations		(254)
Interest rate derivative instruments
Derivative [Line Items]
Amount of unrealized income (loss), net of tax, recognized in other comprehensive (loss) income	$ (4,238)
Amount of unrealized income (loss), net of tax, recognized in other comprehensive (loss) income		$ 7,892