Long-Term Debt - Revolvers - Additional Information (Details) $ in Millions	9 Months Ended
Sep. 30, 2021 USD ($) vessel credit_facility	Dec. 31, 2020 USD ($)
Debt Instrument [Line Items]
Line of credit facility, borrowing capacity, reduction for remainder of year	$ 169.1
Line of credit facility, borrowing capacity, reduction in year two	233.3
Line of credit facility, borrowing capacity, reduction in year three	$ 124.4
Minimum [Member]
Debt Instrument [Line Items]
Variable interest rate on debt	0.60%
Maximum [Member]
Debt Instrument [Line Items]
Variable interest rate on debt	3.25%
Line of Credit
Debt Instrument [Line Items]
Number Of Vessels \| vessel	2
Unsecured Debt
Debt Instrument [Line Items]
Number of credit facilities \| credit_facility	1
Revolving Credit Facilities
Debt Instrument [Line Items]
Line Of Credit Reduction Of Available Borrowing Capacity in Year One	$ 330.4
Revolving Credit Facilities \| Line of Credit
Debt Instrument [Line Items]
Number of credit facilities \| credit_facility	2
Line of credit facility, maximum borrowing capacity	$ 330.4	$ 354.8
Undrawn amount of revolving credit facilities	$ 225.4	$ 254.8
Revolving Credit Facilities \| Line of Credit \| LIBOR \| Minimum [Member]
Debt Instrument [Line Items]
Variable interest rate on debt	1.40%
Revolving Credit Facilities \| Line of Credit \| LIBOR \| Maximum [Member]
Debt Instrument [Line Items]
Variable interest rate on debt	2.25%

Line Of Credit Reduction Of Available Borrowing Capacity in Year One

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- Definition

Number Of Credit Facilities

+ References

No definition available.

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- Definition

Number Of Vessels

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- Definition

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

+ References

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No definition available.

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- 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

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.19(b),22(b))
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- Definition

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

+ References

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Amount of long-term debt payable, sinking fund requirement, and other securities issued that are redeemable by holder at fixed or determinable price and date, maturing in third fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 1E
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-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
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Amount of long-term debt payable, sinking fund requirement, and other securities issued that are redeemable by holder at fixed or determinable price and date, maturing in second fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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Amount of long-term debt payable, sinking fund requirement, and other securities issued that are redeemable by holder at fixed or determinable price and date, maturing in remainder of current fiscal year.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
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-URI http://asc.fasb.org/extlink&oid=120395691&loc=d3e24072-122690

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