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SIGNIFICANT ACCOUNTING POLICIES - INCOME TAXES (Details) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2018 | Jun. 30, 2018
SIGNIFICANT ACCOUNTING POLICIES |  |
Tax Act, income tax expense (benefit) | $ (0.2) | $ 3.1
Sequestration rate (as a percent) |  | 6.20%

X
- Definition Internal Revenue Service sequestration rate on alternative minimum tax refunds. + References No definition available. + Details
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Namespace Prefix: | matx_
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Balance Type: | na
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X
- Definition Amount of income tax expense (benefit) from effect of Tax Cuts and Jobs Act of 2017. + References No definition available. + Details
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Namespace Prefix: | matx_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- References No definition available. + Details
Name: | us-gaap_AccountingPoliciesAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration