CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
CONDENSED CONSOLIDATED BALANCE SHEETS [Abstract]
Unbilled voyage receivable (in dollars)	$ 97,948	$ 74,355
Voyage receivables, allowance for credit losses	1,299	1,245
Vessels and other property, accumulated depreciation	$ 378,747	$ 364,868
Common stock, shares authorized	100,000,000	100,000,000
Common stock, no par value	$ 0	$ 0
Common stock, shares, issued	28,823,465	29,274,452
Common stock, shares, outstanding	28,823,465	29,274,452

Amount of accumulated depreciation, depletion and amortization for physical assets used in the normal conduct of business to produce goods and services.

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Amount of allowance for credit loss on accounts receivable.

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Face amount per share of no-par value common stock.

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The maximum number of common shares permitted to be issued by an entity's charter and bylaws.

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Total number of common shares of an entity that have been sold or granted to shareholders (includes common shares that were issued, repurchased and remain in the treasury). These shares represent capital invested by the firm's shareholders and owners, and may be all or only a portion of the number of shares authorized. Shares issued include shares outstanding and shares held in the treasury.

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Number of shares of common stock outstanding. Common stock represent the ownership interest in a corporation.

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Unbilled amounts due for services rendered or to be rendered, actions taken or to be taken, or a promise to refrain from taking certain actions in accordance with the terms of a legally binding agreement between the entity and, at a minimum, one other party. An example would be amounts associated with contracts or programs where the recognized revenue for performance thereunder exceeds the amounts billed under the terms thereof as of the date of the balance sheet.

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