Operating Segments (Segment Profit And Loss) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2015 segment	Mar. 31, 2014
Segment Reporting Information [Line Items]
Number of operating segments	6us-gaap_NumberOfOperatingSegments
Fixed Revenue	$ 51,281ish_FixedRevenuesFromExternalCustomers	$ 54,943ish_FixedRevenuesFromExternalCustomers
Variable Revenue	16,745	17,751
Total Revenues	68,026us-gaap_Revenues	72,694us-gaap_Revenues
Voyage Expenses	52,211ish_VoyageExpenses	57,433ish_VoyageExpenses
Amortization Expenses	5,187	5,163
Loss (Income) of Unconsolidated Entities	(893)	108
Gross Voyage Profit	11,521ish_GrossVoyageProfit	9,990ish_GrossVoyageProfit
Gross Voyage Profit Margin Percentage (in hundredths)	17.00%ish_GrossVoyageProfitMarginPercentage	14.00%ish_GrossVoyageProfitMarginPercentage
External Customers [Member]
Segment Reporting Information [Line Items]
Total Revenues	68,026	72,694
Jones Act [Member]
Segment Reporting Information [Line Items]
Fixed Revenue	24,595	29,100
Voyage Expenses	18,590	21,209
Amortization Expenses	3,828	3,667
Gross Voyage Profit	2,177	4,224
Gross Voyage Profit Margin Percentage (in hundredths)	9.00%	15.00%
Jones Act [Member] \| External Customers [Member]
Segment Reporting Information [Line Items]
Total Revenues	24,595	29,100
PCTC [Member]
Segment Reporting Information [Line Items]
Fixed Revenue	14,247	15,615
Variable Revenue	7,533	3,941
Voyage Expenses	17,020	16,663
Amortization Expenses	715	535
Gross Voyage Profit	4,045	2,358
Gross Voyage Profit Margin Percentage (in hundredths)	19.00%	12.00%
PCTC [Member] \| External Customers [Member]
Segment Reporting Information [Line Items]
Total Revenues	21,780	19,556
Dry Bulk Carriers [Member]
Segment Reporting Information [Line Items]
Fixed Revenue	1,868	1,526
Variable Revenue	1,255	3,590
Voyage Expenses	2,580	3,566
Amortization Expenses	61	77
Loss (Income) of Unconsolidated Entities	(635)	80
Gross Voyage Profit	1,117	1,393
Gross Voyage Profit Margin Percentage (in hundredths)	36.00%	27.00%
Dry Bulk Carriers [Member] \| External Customers [Member]
Segment Reporting Information [Line Items]
Total Revenues	3,123	5,116
Rail-Ferry Service [Member]
Segment Reporting Information [Line Items]
Variable Revenue	7,785	7,926
Voyage Expenses	6,886	6,846
Amortization Expenses	285	160
Loss (Income) of Unconsolidated Entities	74	28
Gross Voyage Profit	540	892
Gross Voyage Profit Margin Percentage (in hundredths)	7.00%	11.00%
Rail-Ferry Service [Member] \| External Customers [Member]
Segment Reporting Information [Line Items]
Total Revenues	7,785	7,926
Specialty Contracts [Member]
Segment Reporting Information [Line Items]
Fixed Revenue	10,571	8,702
Variable Revenue	185	2,248
Voyage Expenses	7,557	9,476
Amortization Expenses	298	724
Loss (Income) of Unconsolidated Entities	(332)
Gross Voyage Profit	3,233	750
Gross Voyage Profit Margin Percentage (in hundredths)	30.00%	7.00%
Specialty Contracts [Member] \| External Customers [Member]
Segment Reporting Information [Line Items]
Total Revenues	10,756	10,950
Other [Member]
Segment Reporting Information [Line Items]
Variable Revenue	(13)	46
Voyage Expenses	(422)	(327)
Gross Voyage Profit	409	373
Other [Member] \| External Customers [Member]
Segment Reporting Information [Line Items]
Total Revenues	$ (13)	$ 46

Amortization Of Intangible Assets And Dry Dock

No definition available.

Name:	ish_AmortizationOfIntangibleAssetsAndDryDock
Namespace Prefix:	ish_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of fixed revenue from external customers for the reportable segment. Such disclosure is presented if the amount is: (a) included in the measure of segment profit or loss reviewed by the chief operating decision maker or (b) otherwise regularly provided to the chief operating decision maker, even if not included in that measure of segment profit or loss.

+ References

No definition available.

+ Details

Name:	ish_FixedRevenuesFromExternalCustomers
Namespace Prefix:	ish_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Aggregate revenue less cost of goods and services sold or operating expenses directly attributable to the revenue generation activity.

+ References

No definition available.

+ Details

Name:	ish_GrossVoyageProfit
Namespace Prefix:	ish_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Refers to Gross Voyage Profit Margin Percentage.

+ References

No definition available.

+ Details

Name:	ish_GrossVoyageProfitMarginPercentage
Namespace Prefix:	ish_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of variable revenue from external customers for the reportable segment. Such disclosure is presented if the amount is: (a) included in the measure of segment profit or loss reviewed by the chief operating decision maker or (b) otherwise regularly provided to the chief operating decision maker, even if not included in that measure of segment profit or loss.

+ References

No definition available.

+ Details

Name:	ish_VariableRevenuesFromExternalCustomers
Namespace Prefix:	ish_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Expenses associated with operating vessels which are attributable to particular voyages.

+ References

No definition available.

+ Details

Name:	ish_VoyageExpenses
Namespace Prefix:	ish_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

This item represents the entity's proportionate share for the period of the net income (loss) of its investee (such as unconsolidated subsidiaries and joint ventures) to which the equity method of accounting is applied. This item includes income or expense related to stock-based compensation based on the investor's grant of stock to employees of an equity method investee.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 28

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 9

-Article 5

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 323

-SubTopic 10

-Section 45

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=16385135&loc=d3e33749-111570

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 225

-SubTopic 10

-Section S99

-Paragraph 2

-Subparagraph (SX 210.5-03.12)

-URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688

Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Paragraph 11

-Article 7

+ Details

Name:	us-gaap_IncomeLossFromEquityMethodInvestments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Number of operating segments. An operating segment is a component of an enterprise: (a) that engages in business activities from which it may earn revenues and incur expenses (including revenues and expenses relating to transactions with other components of the same enterprise), (b) whose operating results are regularly reviewed by the enterprise's chief operating decision maker to make decisions about resources to be allocated to the segment and assess its performance, and (c) for which discrete financial information is available. An operating segment may engage in business activities for which it has yet to earn revenues, for example, start-up operations may be operating segments before earning revenues.

+ References

No definition available.

+ Details

Name:	us-gaap_NumberOfOperatingSegments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 225

-SubTopic 10

-Section S99

-Paragraph 2

-Subparagraph (SX 210.5-03.1)

-URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 1

-Article 5

+ Details

Name:	us-gaap_Revenues
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

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

- Details

Name:	us-gaap_MajorCustomersAxis=ish_ExternalCustomersMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=ish_DryBulkCarriersMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=ish_JonesActMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=ish_RailFerryServiceMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=ish_SpecialtyContractsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=us-gaap_CorporateAndOtherMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=us-gaap_TrucksMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: