Lines of Credit and Financing Arrangements (Senior Unsecured Notes) (Details) - Senior Unsecured Notes [Member] - USD ($)	12 Months Ended
Dec. 31, 2019	Nov. 01, 2016
Debt Instrument [Line Items]
Debt issued		$ 350,000,000.0
Fixed interest rate for senior unsecured notes		3.00%
Minimum amount of principal or interest due on indebtedness or receivable securitization	$ 75,000,000
Number of days within notice date acceleration is not rescinded	30 days

Debt Instrument, Cross Default Provision, Maximum Term if Acceleration is not Rescinded

No definition available.

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Namespace Prefix:	lii_
Data Type:	xbrli:durationItemType
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Period Type:	duration

- Definition

Minimum amount of principal or interest due on indebtedness or receivable securitization.

+ References

No definition available.

+ Details

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Namespace Prefix:	lii_
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Balance Type:	credit
Period Type:	duration

- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=114775744&loc=d3e28551-108399

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=114775985&loc=d3e28878-108400

+ Details

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

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- 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

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Balance Type:	na
Period Type:	duration

- Details

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