Share-based compensation - Schedule of Information about Three Tranches of SARs Granted (Detail) - $ / shares	12 Months Ended
Dec. 31, 2015	Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of SARs		1,664,457
Tranche 1 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Base price	$ 21.50
Expiration date	Dec. 07, 2015
Number of SARs		531,885
Tranche 2 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Base price	$ 24.00
Expiration date	Dec. 07, 2016
Number of SARs		556,946
Tranche 3 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Base price	$ 26.50
Expiration date	Dec. 07, 2017
Number of SARs		575,626

Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Grants In Period Base Price

No definition available.

+ Details

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Namespace Prefix:	ssw_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration

- 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).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(iii)(1)
-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

+ Details

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Balance Type:	na
Period Type:	duration

- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)(2)
-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

+ Details

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- Definition

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.

+ References

No definition available.

+ Details

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- Details

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- Details

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