Employee Benefit Plans (Multi-Employer Pension And Other Postretirement Benefit Plans) (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2015	Dec. 31, 2014
Multiemployer Plans [Line Items]
Contribution Amount	$ 2,516	$ 2,748
WSC [Member] \| MM&P [Member]
Multiemployer Plans [Line Items]
Contribution Amount	$ 486	609
Surcharge Imposed	No
Expiration Date, First	Sep. 30, 2025
Expiration Date, Last	Sep. 30, 2025
WSC [Member] \| MEBA [Member]
Multiemployer Plans [Line Items]
Contribution Amount	$ 235	272
Surcharge Imposed	No
Expiration Date, Last	Sep. 30, 2020
WSC [Member] \| ARA [Member]
Multiemployer Plans [Line Items]
Surcharge Imposed	No
WSC [Member] \| SPP [Member]
Multiemployer Plans [Line Items]
Contribution Amount	$ 74	86
Surcharge Imposed	No
Expiration Date, First	Sep. 30, 2017
Expiration Date, Last	Dec. 31, 2016
SCI [Member] \| MM&P [Member]
Multiemployer Plans [Line Items]
Contribution Amount	$ 369	378
Expiration Date, Last	Jun. 30, 2027
SCI [Member] \| MEBA [Member]
Multiemployer Plans [Line Items]
Contribution Amount	$ 143	127
SCI [Member] \| SPP [Member]
Multiemployer Plans [Line Items]
Contribution Amount	$ 81	85
Expiration Date, Last	Jun. 30, 2017
CGL [Member] \| MM&P [Member]
Multiemployer Plans [Line Items]
Contribution Amount	$ 700	790
Expiration Date, First	Sep. 30, 2025
Expiration Date, Last	Jun. 30, 2020
CGL [Member] \| MEBA [Member]
Multiemployer Plans [Line Items]
Contribution Amount	$ 281	257
Expiration Date, First	Sep. 30, 2020
Expiration Date, Last	Jun. 30, 2020
CGL [Member] \| ARA [Member]
Multiemployer Plans [Line Items]
Contribution Amount	$ 54	54
Expiration Date, First	Sep. 30, 2015
Expiration Date, Last	Jun. 30, 2017
CGL [Member] \| SPP [Member]
Multiemployer Plans [Line Items]
Contribution Amount	$ 93	$ 90
Expiration Date, First	Dec. 31, 2016
Expiration Date, Last	Jun. 30, 2017

Amount of contributions made to multiemployer plans by the employer. A multiemployer plan is a pension or postretirement benefit plan to which two or more unrelated employers contribute where assets contributed by one participating employer may be used to provide benefits to employees of other participating employers.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 80
-Section 50
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=35742057&loc=SL14450702-114947

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 80
-Section 50
-Paragraph 9
-URI http://asc.fasb.org/extlink&oid=35742057&loc=SL14450691-114947

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 80
-Section 50
-Paragraph 5
-Subparagraph (e)(1)
-URI http://asc.fasb.org/extlink&oid=35742057&loc=SL14450657-114947

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Expiration date of the collective bargaining arrangement requiring contributions to the multiemployer plan that will expire first in a group of associated collective bargaining arrangements, in CCYY-MM-DD format. A multiemployer plan is a pension or postretirement benefit plan to which two or more unrelated employers contribute where assets contributed by one participating employer may be used to provide benefits to employees of other participating employers.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 80
-Section 50
-Paragraph 5
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=35742057&loc=SL14450657-114947

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

Expiration date of the collective bargaining arrangement requiring contributions to the multiemployer plan that will expire last in a group of associated collective bargaining arrangements, in CCYY-MM-DD format. A multiemployer plan is a pension or postretirement benefit plan to which two or more unrelated employers contribute where assets contributed by one participating employer may be used to provide benefits to employees of other participating employers.

+ References

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- 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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Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Indicate whether the employer paid a surcharge to the pension or postretirement benefit plan to which two or more unrelated employers contribute where assets contributed by one participating employer may be used to provide benefits to employees of other participating employers. The acceptable values are "no", "yes", and "NA".

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 80
-Section 50
-Paragraph 5
-Subparagraph (f)(2)
-URI http://asc.fasb.org/extlink&oid=35742057&loc=SL14450657-114947

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	us-types:surchargeItemType
Balance Type:	na
Period Type:	duration

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MultiemployerPlanNameAxis=ish_MastersMatesAndPilotsPensionPlanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MultiemployerPlanNameAxis=ish_MebaPensionTrustMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MultiemployerPlanNameAxis=ish_AmericanRadioAssociationPensionTrustMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MultiemployerPlanNameAxis=ish_SeafarersPensionPlanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=ish_SciMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=ish_CglMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: