DESCRIPTION OF THE BUSINESS (Details)	9 Months Ended
	Sep. 30, 2018 segment facility
DESCRIPTION OF THE BUSINESS
Number of reportable segments | segment	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	4