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Selected Quarterly Financial Information (unaudited) (Textuals) (Details) - USD ($) $ in Millions | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2019 | Sep. 30, 2019 | Jun. 30, 2019 | Dec. 31, 2019
Quarterly Financial Information Disclosure [Abstract] |  |  |  |
Net Loss(gain) from natural disaster, net of Insurance recoveries | $ 93.4 | $ 7.1 | $ 31.9 | $ 46.4
Gain from insurance recoveries, net of losses incurred | $ 93.4 | $ 7.1 | $ 31.9 | $ 46.4

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- Definition Net Loss(gain) from natural disaster, net of Insurance recoveries + References No definition available. + Details
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Namespace Prefix: | lii_
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Balance Type: | debit
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- References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
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