Commitments and Contingencies - Charge-backs for Various Contracts (Details) $ in Millions	Dec. 31, 2018 USD ($)
Commitments and Contingencies Disclosure [Abstract]
2019	$ 30.7
2020	16.0
2021	6.6
2022	2.2
2023	0.5
Thereafter	0.0
Total	$ 56.0

- Definition

Amount of estimated contractual obligations to be paid in the next fiscal year following the latest fiscal year related to the cancellation of various contracts.

+ References

No definition available.

+ Details

Name:	lad_ChargeBacksFutureMinimumPaymentsCurrent
Namespace Prefix:	lad_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of estimated contractual obligations to be paid in the fifth fiscal year following the latest fiscal year related to the cancellation of various contracts

+ References

No definition available.

+ Details

Name:	lad_ChargeBacksFutureMinimumPaymentsDueInFiveYears
Namespace Prefix:	lad_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of estimated contractual obligations to be paid in the fourth fiscal year following the latest fiscal year related to the cancellation of various contracts

+ References

No definition available.

+ Details

Name:	lad_ChargeBacksFutureMinimumPaymentsDueInFourYears
Namespace Prefix:	lad_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of estimated contractual obligations to be paid in the third fiscal year following the latest fiscal year related to the cancellation of various contracts.

+ References

No definition available.

+ Details

Name:	lad_ChargeBacksFutureMinimumPaymentsDueInThreeYears
Namespace Prefix:	lad_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of estimated contractual obligations to be paid in the second fiscal year following the latest fiscal year related to the cancellation of various contracts.

+ References

No definition available.

+ Details

Name:	lad_ChargeBacksFutureMinimumPaymentsDueInTwoYears
Namespace Prefix:	lad_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of estimated contractual obligations to be paid after the fifth fiscal year following the latest fiscal year related to the cancellation of various contracts.

+ References

No definition available.

+ Details

Name:	lad_ChargeBacksFutureMinimumPaymentsDueThereafter
Namespace Prefix:	lad_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The amount of liabilities pertaining to charge backs.

+ References

No definition available.

+ Details

Name:	lad_ChargeBacksLiabilities
Namespace Prefix:	lad_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- References

No definition available.

+ Details

Name:	us-gaap_CommitmentsAndContingenciesDisclosureAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration