The maximum par or stated value of common shares permitted to be issued by an entity's charter and bylaws.

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Increase in authorised common stock

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Number of Container Vessels accounted for as right of use assets

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Own-share Lending Arrangement, Shares, Total Authorised for share lending arrangement

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Shares issued on conversion of convertible debt

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Adjustment to additional paid in capital resulting from the recognition of convertible debt instruments as two separate components - a debt component and an equity component. This bifurcation may result in a basis difference associated with the liability component that represents a temporary difference for purposes of applying accounting for income taxes. The initial recognition of deferred taxes for the tax effect of that temporary difference is as an adjustment to additional paid in capital.

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The amount of subsequent adjustments to additional paid in capital for convertible financial instruments where a component of equity and a component of debt are recognized.

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Face amount or stated value per share of 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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The value of the financial instrument(s) that the original debt is being converted into in a noncash (or part noncash) transaction. "Part noncash" refers to that portion of the transaction not resulting in cash receipts or cash payments in the period.

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The price per share of the conversion feature embedded in the debt instrument.

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

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

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Amount of paid and unpaid common stock dividends declared with the form of settlement in cash, stock and payment-in-kind (PIK).

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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The number of shares issued in connection with an own-share lending arrangement entered into by the entity, in contemplation of a convertible debt offering or other financing.

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The cash outflow during the period from the repayment of aggregate short-term and long-term debt. Excludes payment of capital lease obligations.

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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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The weighted-average price as of the balance sheet date at which grantees can acquire the shares reserved for issuance on vested portions of options outstanding and currently exercisable under the stock option plan.

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Number of shares of stock issued during the period as part of a transaction to acquire assets that do not qualify as a business combination.

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Number of share options (or share units) exercised during the current period.

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SHARE CAPITAL, ADDITIONAL PAID-IN CAPITAL AND CONTRIBUTED SURPLUS (Narrative) (Details)	1 Months Ended				12 Months Ended
	May 31, 2018 containership shares	Apr. 30, 2018 USD ($) $ / shares shares	Feb. 28, 2018 USD ($)	Oct. 31, 2017 USD ($) shares	Dec. 31, 2019 USD ($) containership $ / shares shares	Dec. 31, 2018 USD ($) containership $ / shares shares	Dec. 31, 2017 USD ($) $ / shares shares	Sep. 30, 2018 USD ($) shares	Jun. 30, 2018 vessel	May 04, 2018 USD ($)	Apr. 23, 2018 USD ($) $ / shares shares	Nov. 30, 2016 shares	Oct. 31, 2016 shares	Oct. 05, 2016 USD ($) $ / shares
Share Capital Details
Options exercised (in shares) \| shares					18,246	0	7,500
Share capital, par value (in dollars per share) \| $ / shares		$ 0.01			$ 0.01	$ 0.01
Exercisable at end of year (in dollars per share) \| $ / shares					$ 9.92
Common stock, value authorized					$ 2,000,000	$ 2,000,000		$ 1,500,000
Share Capital, shares authorized (in shares) \| shares					200,000,000	200,000,000		150,000,000
Increase in authorised common stock \| shares						50,000,000
Shares acquired (in shares) \| shares	4,024,984					4,024,984
Number of vessels acquired	4				7	4			15
Total authorised for share lending arrangement (in shares) \| shares		7,000,000
Long-term debt					$ 1,627,177,000	$ 1,460,347,000
Senior Unsecured Convertible Bonds due 2023
Share Capital Details
Interest rate		4.875%			4.875%
Amount of debt repurchased					$ 3,400,000	12,300,000
Adjustment to equity component of convertible bonds arising from reacquisition of bonds					(200,000)	(600,000)
Senior Unsecured Convertible Bonds Due 2018
Share Capital Details
Long-term debt			$ 63,200,000
Senior Unsecured Convertible Bonds due 2021
Share Capital Details
Common stock, shares loaned to affiliate (in shares) \| shares												8,000,000
Recognition of equity component arising from issuance of 4.875% convertible bonds due 2023					4,000,000.0	4,000,000.0
Amount of debt repurchased					0.0	12,800,000
Adjustment to equity component of convertible bonds arising from reacquisition of bonds					$ (0.0)	(500,000)
Debt amount														$ 225,000,000
Conversion price (in dollars per share) \| $ / shares					$ 15.28									$ 17.7747
Additional paid-in capital \| Senior Unsecured Convertible Bonds due 2021
Share Capital Details
Recognition of equity component arising from issuance of 4.875% convertible bonds due 2023					$ 4,600,000
Contributed surplus
Share Capital Details
Dividends, Common Stock					$ (31,939,000)	$ 0	$ 0
Stock Options
Share Capital Details
Options exercised (in shares) \| shares					65,000	0	7,500
Exercisable at end of year (in dollars per share) \| $ / shares					$ 9.58	$ 10.03	$ 11.43
Senior Unsecured Convertible Bonds due 2021
Share Capital Details
Interest rate					5.75%								5.75%
Long-term debt					$ 212,230,000	$ 212,230,000
Shares issued on conversion of convertible debt (in shares) \| shares					0.065451000								0.0562596000
Senior Unsecured Convertible Bonds due 2023
Share Capital Details
Common stock, shares loaned to affiliate (in shares) \| shares					3,765,842
Interest rate		4.875%
Recognition of equity component arising from issuance of 4.875% convertible bonds due 2023					$ 7,100,000	7,400,000
Long-term debt					$ 148,300,000	151,700,000
Shares issued on conversion of convertible debt (in shares) \| shares					0.0654462000						0.0528157000
Debt amount										$ 14,000,000.0	$ 150,000,000.0
Conversion price (in dollars per share) \| $ / shares					$ 15.28						$ 18.93
Senior Unsecured Convertible Bonds due 2023 \| Additional paid-in capital
Share Capital Details
Recognition of equity component arising from issuance of 4.875% convertible bonds due 2023		$ 7,906,000			$ 0		$ 0
3.25% Senior Unsecured Convertible Bonds Due 2018
Share Capital Details
Interest rate			3.25%
Senior Unsecured Convertible Bonds Due 2018
Share Capital Details
Interest rate			3.25%
Amount of debt repurchased			$ 63,200,000
Shares issued on conversion of convertible debt (in shares) \| shares				9,418,798	651,365
Conversion of principal amount				$ 121,000,000.0
Senior Unsecured Convertible Bonds Due 2018 \| Additional paid-in capital
Share Capital Details
Adjustment to equity component of convertible bonds arising from reacquisition of bonds					$ 0	$ (9,933,000)	$ (16,368,000)