Amount after tax of reclassification adjustment from accumulated other comprehensive income of accumulated gain (loss) realized from derivative instruments designated and qualifying as the effective portion of cash flow hedges and an entity's share of an equity investee's deferred hedging gain (loss).

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Derivative Instruments and Risk Management Activities - Impact of Interest Rate Derivative Instruments (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Derivative [Line Items]
Unrealized gain (loss) arising during the period, net of tax benefit (provision) of ($1,078), $1,542, ($3,570), and $1,308, respectively	$ 3,414	$ (2,570)	$ 11,305	$ (2,180)
Floorplan interest expense
Derivative [Line Items]
Gain (loss) reclassified from other comprehensive income (loss), net of tax			(2,999)	(5,656)
Other interest expense
Derivative [Line Items]
Gain (loss) reclassified from other comprehensive income (loss), net of tax			(390)	(1,154)
Interest rate derivative instruments
Derivative [Line Items]
Unrealized gain (loss) arising during the period, net of tax benefit (provision) of ($1,078), $1,542, ($3,570), and $1,308, respectively			$ 11,305	$ (2,180)