Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Mar. 31, 2018	Jun. 30, 2018
Retained Earnings Adjustments [Line Items]
Unrecognized tax benefits		$ 0.3
Deferred Other Tax Expense (Benefit)		$ 3.8
Accounting Standards Update 2016-16 [Member]
Retained Earnings Adjustments [Line Items]
Cumulative Effect on Retained Earnings, Net of Tax	$ 5.1
Accounting Standards Update 2018-02 [Member]
Retained Earnings Adjustments [Line Items]
Cumulative Effect on Retained Earnings, Net of Tax	$ (22.7)

Tax Cuts and Jobs Act of 2017, Incomplete Accounting, Provisional Income Tax Expense(Benefit)

No definition available.

Name:	lii_TaxCutsandJobsActof2017IncompleteAccountingProvisionalIncomeTaxExpenseBenefit
Namespace Prefix:	lii_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of the cumulative effect on retained earnings net of related income tax effect.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 250
-SubTopic 10
-Section 50
-Paragraph 9
-URI http://asc.fasb.org/extlink&oid=64853466&loc=d3e22663-107794

+ Details

Name:	us-gaap_CumulativeEffectOnRetainedEarningsNetOfTax1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- 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.

+ References

No definition available.

+ Details

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

- Definition

Amount of unrecognized tax benefits.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 15A
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=84230637&loc=SL6600010-109319

+ Details

Name:	us-gaap_UnrecognizedTaxBenefits
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

Name:	us-gaap_AdjustmentsForNewAccountingPronouncementsAxis=us-gaap_AccountingStandardsUpdate201616Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AdjustmentsForNewAccountingPronouncementsAxis=lii_AccountingStandardsUpdate201802Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: