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Derivative Instruments and Risk Management Activities - Narrative (Details)	3 Months Ended
	Mar. 31, 2019 USD ($) swap	Mar. 31, 2018 USD ($)	Dec. 31, 2018 USD ($)
Derivative [Line Items]
Gain (loss) related to hedge ineffectiveness	$ 0	$ 0
Increase (decrease) in floor plan interest expense due to impact of interest rate hedges	(300,000)	1,700,000
Floor plan interest expense	15,703,000	$ 14,087,000
Maximum notional value of derivatives in effect at any time	902,400,000
Accumulated unrealized gains (losses), net of income taxes	4,400,000		$ 8,700,000
Amount expected to be reclassified from other comprehensive loss into earnings	$ 2,400,000
Interest Rate Swaps
Derivative [Line Items]
Number of additional forward interest rate swaps | swap	26
Notional value	$ 902,400,000
Weighted average interest rate	2.30%
Forward Interest Rate Swaps
Derivative [Line Items]
Number of additional forward interest rate swaps | swap	2
Notional value	$ 125,000,000
Weighted average interest rate	1.80%

X

- Definition

Interest expense incurred on borrowings under the floorplan line of the credit facility and arrangements with vehicle manufacturer affiliates for the financing of specific new, used and rental vehicle inventory. Interest expense also includes the net impact of interest rate swap settlements during the period, which are designed to hedge exposure to variable interest rates.

+ References

No definition available.

+ Details

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X

- Definition

The increase or decrease in floorplan interest expense due to interest rate hedges.

+ References

No definition available.

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- Definition

Maximum notional amount of derivatives in effect at any time.

+ References

No definition available.

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- Definition

Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 13
-Sentence Column B

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- Definition

Accumulated change, net of tax, in accumulated gains and losses from derivative instruments designated and qualifying as the effective portion of cash flow hedges. Includes an entity's share of an equity investee's Increase or Decrease in deferred hedging gains or losses.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=114867106&loc=d3e637-108580

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-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 10A
-Subparagraph (d)
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-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 14
-URI http://asc.fasb.org/extlink&oid=114867106&loc=d3e681-108580

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- Definition

Average fixed interest rate related to the group of interest rate derivatives.

+ References

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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- Definition

The number of derivative instruments of a particular group held by the entity.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1A
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- Definition

The net gain (loss) recognized in earnings during the reporting period representing the amount of the cash flow hedges' ineffectiveness.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 10
-Section 50
-Paragraph 4C
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- Definition

The estimated net amount of unrealized gains or losses on interest rate cash flow hedges as of the balance sheet date expected to be reclassified to earnings within the next twelve months.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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-SubTopic 30
-Section 50
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