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DESCRIPTION OF THE BUSINESS (Details) | 3 Months Ended
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Mar. 31, 2021 facility segment | Mar. 31, 2020 segment
DESCRIPTION OF THE BUSINESS |  |
Number of reportable segments | segment | 2 | 2
Ocean Transportation | SSAT |  |
DESCRIPTION OF THE BUSINESS |  |
Ownership interest in SSAT (as a percent) | 35.00% |
Number of terminal facilities on which SSAT provided terminal and stevedoring services on the U.S. West Coast | 7 |
MatNav | SSAT |  |
DESCRIPTION OF THE BUSINESS |  |
Number of terminal facilities on which SSAT provided terminal and stevedoring services on the U.S. West Coast | 3 |

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