Common shares to be issued upon exercise of stock options.

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Purchase of common shares.

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Share based compensation arrangement by share based payment award renewed date.

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Share-based compensation arrangement by share-based payment award vesting start date.

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Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

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Amount of cost not yet recognized for nonvested award under share-based payment arrangement.

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Weighted-average period over which cost not yet recognized is expected to be recognized for award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

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Period over which grantee's right to exercise award under share-based payment arrangement is no longer contingent on satisfaction of service or performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, combination of market, performance or service condition.

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Description of service or performance condition required to be met for earning right to award under share-based payment arrangement. Includes, but is not limited to, combination of market, performance or service condition.

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Description of terms of share-based payment arrangement. Includes, but is not limited to, type of award or grantee and reason for issuance.

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- Definition

The number of equity-based payment instruments, excluding stock (or unit) options, that were forfeited during the reporting period.

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- Definition

The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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- Definition

The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period.

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- Definition

Date the equity-based award expires, in CCYY-MM-DD format.

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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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No definition available.

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Number of shares authorized for issuance under share-based payment arrangement.

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- Definition

The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

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- Definition

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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- Definition

Gross number of share options (or share units) granted during the period.

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No definition available.

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Number of fully vested and expected to vest exercisable options that may be converted into shares under option plan. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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- Definition

Per share or per unit amount of equity securities issued.

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No definition available.

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Share-based compensation - Additional Information (Detail) - Seaspan [Member] - USD ($)	1 Months Ended					12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018	Jan. 31, 2018	Aug. 31, 2017	Jul. 31, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2015
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total shares of common stock reserved for issuance under the plan								5,000,000	3,000,000
Remaining shares left for issuance under this plan		2,187,420				1,291,076	2,187,420
Share-based compensation expenses						$ 3,310,000	$ 2,989,000	$ 10,400,000
Total unrecognized compensation costs relating to unvested share-based compensation awards		$ 1,474,000				$ 3,764,000	$ 1,474,000
Expected to be recognized over a weighted average period						22 months	22 months
Restricted shares [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting period						1 year
Granted, stock units						107,400	664,326	107,270
Vested, stock units						185,742	119,509	56,861
Cancelled, stock units						0	53,608	12,737
Phantom share units [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting period						3 years
Granted, stock units						0	30,000	90,000
Vested, stock units						0	0	0
Cancelled, stock units						0	76,666	0
Restricted stock units [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting period						3 years
Granted, stock units						209,732	109,248	88,293
Vested, stock units						124,073	83,220	537,216
Retention requirement description						The restricted stock units generally vest over three years, in equal one-third amounts on each anniversary date of the date of the grant.
Renewed date						Jul. 01, 2018
Cancelled, stock units						33,466	12,441	3,280
Stock options [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Granted, stock units						0	500,000	0
Vested, stock units						0	0	0
Cancelled, stock units						0	0	0
Chief Executive Officer [Member] \| Restricted shares [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting period		5 years
Granted, stock units		500,000
Vested, stock units						100,000
Cancelled, stock units	100,000
Chief Executive Officer [Member] \| Stock options [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting period			5 years
Stock options, vesting description			The stock options vest equally on each of the first five anniversaries of the CEO’s start date in January 2018 and expire on January 8, 2028. As at December 31, 2019, 100,000 of these stock options are vested and exercisable.
Stock options, vesting start date			Jan. 31, 2018
Expiration date			Jan. 08, 2028
Stock options, vested and exercisable						100,000
Class A Common Shares [Member] \| Chairman [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation expenses								$ 6,920,000
Common shares granted					1,000,000
Purchase of common shares by chairman				1,000,000
Common shares purchased, price per share				$ 6.00
Class A Common Shares [Member] \| Chief Executive Officer [Member] \| Stock options [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares issuable upon exercise of options			500,000
Stock options, exercise price			$ 7.20