OPERATING REVENUES - Contract Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Capitalized Contract Cost [Line Items]
Contract assets	$ 81,753	$ 120,158
Voyages in progress
Capitalized Contract Cost [Line Items]
Contract assets	26,021	59,437
Trade accounts receivable
Capitalized Contract Cost [Line Items]
Contract assets	42,104	52,278
Related party receivables
Capitalized Contract Cost [Line Items]
Contract assets	9,137	3,084
Other current assets
Capitalized Contract Cost [Line Items]
Contract assets	$ 4,491	$ 5,359

Amount, before allowance for credit loss, of right to consideration in exchange for good or service transferred to customer when right is conditioned on something other than passage of time, classified as current.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=118944033&loc=SL49130531-203044

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 45
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=118944033&loc=SL49130533-203044

Name:	us-gaap_ContractWithCustomerAssetGrossCurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant