Fair Value Measurements - Summary of Fair Value and Carrying Value of Assets and Liabilities Measured on Recurring and Non-recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets (note 10)	$ 4,226	$ 4,538
Advances to equity accounted investments	9,930	10,480
Long-term debt, including current portion	(963,247)	(941,661)
Reported Value Measurement \| Equity accounted investments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Advances to equity accounted investments	9,930	10,480
Reported Value Measurement \| Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, including current portion	(952,302)	(933,016)
Obligations related to capital leases, including current portion	(148,908)
Reported Value Measurement \| Fair Value, Measurements, Recurring \| Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents and restricted cash	75,710	94,907
Reported Value Measurement \| Fair Value, Measurements, Recurring \| Level 2 \| Interest Rate Swap
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Interest rate swap agreements	5,242	3,143
Reported Value Measurement \| Fair Value, Measurements, Recurring \| Level 3 \| Time-charter Swap
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets (note 10)	0	875
Reported Value Measurement \| Fair Value, Measurements, Recurring \| Level 3 \| Warrant
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets (note 10)	0	287
Reported Value Measurement \| Fair Value, Measurements, Non-recurring \| Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Vessels held for sale	0	33,802
Fair Value Asset/(Liability) \| Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, including current portion	(946,105)	(923,306)
Obligations related to capital leases, including current portion	(147,401)
Fair Value Asset/(Liability) \| Fair Value, Measurements, Recurring \| Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents and restricted cash	75,710	94,907
Fair Value Asset/(Liability) \| Fair Value, Measurements, Recurring \| Level 2 \| Interest Rate Swap
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Interest rate swap agreements	5,242	3,143
Fair Value Asset/(Liability) \| Fair Value, Measurements, Recurring \| Level 3 \| Time-charter Swap
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets (note 10)	0	875
Fair Value Asset/(Liability) \| Fair Value, Measurements, Recurring \| Level 3 \| Warrant
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets (note 10)	0	287
Fair Value Asset/(Liability) \| Fair Value, Measurements, Non-recurring \| Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Vessels held for sale	$ 0	$ 33,802

Long-Term advances receivable from a party that is affiliated with the reporting entity by means of direct or indirect ownership. This does not include advances to clients.

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-Name Accounting Standards Codification
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Fair value portion of assets classified as held for sale.

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Amount equal to the present value (the principal) at the beginning of the lease term of minimum lease payments during the lease term (excluding that portion of the payments representing executory costs such as insurance, maintenance, and taxes to be paid by the lessor, together with any profit thereon) net of payments or other amounts applied to the principal through the balance sheet date.

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Amount of cash and cash equivalents, and cash and cash equivalents restricted to withdrawal or usage. Excludes amount for disposal group and discontinued operations. Cash includes, but is not limited to, currency on hand, demand deposits with banks or financial institutions, and other accounts with general characteristics of demand deposits. Cash equivalents include, but are not limited to, short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

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Fair value as of the balance sheet date of derivative instrument not designated as hedging instrument and classified as an asset.

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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.

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Fair value as of the balance sheet date of all derivatives not designated as hedging instruments.

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