The additional interest rate based on the entity's consolidated leverage ratio.

No definition available.

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- Definition

Covenant threshold for debt incurred based on the aggregate principal amount of priority debt.

+ References

No definition available.

+ Details

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Period Type:	instant

- Definition

Covenant for minimum working capital.

+ References

No definition available.

+ Details

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Balance Type:	debit
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- Definition

Debt instrument covenant, long-term debt to net worth.

+ References

No definition available.

+ Details

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- Definition

Debt instrument covenant ratio, maintenance of net worth.

+ References

No definition available.

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- Definition

Number of consecutive quarters for measuring the leverage ratio per credit agreement.

+ References

No definition available.

+ Details

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- Definition

Represents the actual consolidated interest coverage ration used to determine compliance with the financial covenant of the line of credit facility.

+ References

No definition available.

+ Details

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- Definition

Represents the option to increase the revolving credit facility.

+ References

No definition available.

+ Details

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Period Type:	instant

- Definition

Amount of semi-annual principal payments that the company has to pay after year five since the first year of maturity payment as stated in the agreement.

+ References

No definition available.

+ Details

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- Definition

Amount of semi-annual principal payments that the company has to pay in the year one as stated in the agreement.

+ References

No definition available.

+ Details

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- Definition

Amount of semi-annual principal payments that the company has to pay in year two to year five since the first year of maturity payment as stated in the agreement.

+ References

No definition available.

+ Details

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- Definition

The number of vessels committed to securing debt.

+ References

No definition available.

+ Details

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- Definition

Amount of the total principal payments made during the annual reporting period.

+ References

+ Details

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Data Type:	xbrli:monetaryItemType
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- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

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- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
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- Definition

The average effective interest rate during the reporting period.

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- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

+ Details

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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Balance Type:	na
Period Type:	duration

- Definition

Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

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Period Type:	duration

- Definition

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- Definition

The fee, expressed as a percentage of the line of credit facility, for the line of credit facility regardless of whether the facility has been used.

+ References

No definition available.

+ Details

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Data Type:	num:percentItemType
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Period Type:	duration

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

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Period Type:	instant

- Definition

Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding).

+ References

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The fee, expressed as a percentage of the line of credit facility, for available but unused credit capacity under the credit facility.

+ References

No definition available.

+ Details

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Data Type:	num:percentItemType
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- References

No definition available.

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- Definition

The cash outflow for loan and debt issuance costs.

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-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
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-Paragraph 15
-URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3291-108585

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DEBT - REVOLVING CREDIT FACILITY (Details)					12 Months Ended
DEBT - REVOLVING CREDIT FACILITY (Details)	Jun. 22, 2020 USD ($)	Apr. 27, 2020 USD ($)	Mar. 31, 2020 item	Sep. 14, 2016 USD ($)	Dec. 31, 2020 USD ($) item
Debt
Payment of debt financing costs					$ 18,500,000
Title XI Notes
Debt
The number of vessels committed to securing debt \| item					2
Revolving Credit Facility
Debt
Maximum borrowing capacity under revolving credit facility					$ 650,000,000
Uncommitted option to increase credit facility					250,000,000
Funds available under the revolving credit facility					$ 570,100,000
Interest rate during period (as a percent)					2.50%
Covenant threshold for debt incurred					$ 331,000,000
Revolving Credit Facility \| Minimum
Debt
Credit facility commitment fee percentage			0.25%
Ratio of consolidated EBITDA to interest expense					3.50
Revolving Credit Facility \| Maximum
Debt
Credit facility commitment fee percentage			0.55%
Standby and commercial letters of credit
Debt
Maximum borrowing capacity under revolving credit facility					$ 100,000,000
Standby letters of credit					8,100,000
Standby and commercial letters of credit \| Minimum
Debt
Line of credit fees percentage			1.75%
Standby and commercial letters of credit \| Maximum
Debt
Line of credit fees percentage			3.50%
Swing Line Loans
Debt
Maximum borrowing capacity under revolving credit facility					50,000,000
The Senior Unsecured Notes (The "Series D Notes")
Debt
Debt issued				$ 200,000,000.0
Interest rate (as a percent)				3.14%
Debt instrument term				15 years
Maturities of Long-term Debt
Semi-annual principal payments in year 2019				$ 6,000,000.0
Semi-annual principal payments in 2020 to 2023				9,200,000
Semi-annual principal payments in 2024 to 2031				$ 7,150,000
Private Loan Facilities
Debt
Number of consecutive quarters \| item			2
Additional interest rate based on the entity's consolidated leverage ratio			25.00%
London Interbank Offered Rate (LIBOR) \| Revolving Credit Facility \| Minimum
Debt
Variable rate margin			1.75%
London Interbank Offered Rate (LIBOR) \| Revolving Credit Facility \| Maximum
Debt
Variable rate margin			3.50%
Base rate \| Revolving Credit Facility \| Minimum
Debt
Variable rate margin			0.75%
Base rate \| Revolving Credit Facility \| Maximum
Debt
Variable rate margin			2.50%
MatNav \| Title XI Notes
Debt
Minimum working capital covenant					$ 1
Debt instrument covenant ratio, maintenance of net worth					90.00%
Payment of debt financing costs	$ 6,700,000	$ 8,700,000
Debt issued	$ 139,600,000	$ 185,900,000
Interest rate (as a percent)	1.35%	1.22%
Annual principal payments	$ 3,000,000.0	$ 4,000,000.0
MatNav \| Minimum \| Title XI Notes
Debt
Debt instrument covenant, long-term debt to net worth					2.00%