Operating Segments (Segment Profit And Loss) (Details) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2015 USD ($)	Jun. 30, 2014 USD ($)	Jun. 30, 2015 USD ($) segment	Jun. 30, 2014 USD ($)
Segment Reporting Information [Line Items]
Number of operating segments \| segment			6
Fixed Revenue	$ 47,001	$ 58,756	$ 98,282	$ 113,698
Variable Revenue	20,307	17,996	37,052	35,748
Total Revenues	67,308	76,752	135,334	149,446
Voyage Expenses	53,809	57,802	106,020	115,235
Amortization Expenses	4,348	5,486	9,535	10,649
Loss (Income) of Unconsolidated Entities	(665)	80	(1,558)	188
Gross Voyage Profit (excluding Depreciation Expense)	$ 9,816	$ 13,384	$ 21,337	$ 23,374
Gross Voyage Profit Margin Percentage (in hundredths)	15.00%	17.00%	16.00%	16.00%
Jones Act [Member]
Segment Reporting Information [Line Items]
Fixed Revenue	$ 19,550	$ 33,216	$ 44,145	$ 62,315
Total Revenues	19,550	33,216	44,145	62,315
Voyage Expenses	16,702	23,503	35,292	44,712
Amortization Expenses	3,114	3,678	6,942	7,345
Gross Voyage Profit (excluding Depreciation Expense)	$ (266)	$ 6,035	$ 1,911	$ 10,258
Gross Voyage Profit Margin Percentage (in hundredths)	(1.00%)	18.00%	4.00%	16.00%
PCTC [Member]
Segment Reporting Information [Line Items]
Fixed Revenue	$ 14,512	$ 15,295	$ 28,759	$ 30,911
Variable Revenue	8,656	3,858	16,189	7,799
Total Revenues	23,168	19,153	44,948	38,710
Voyage Expenses	18,041	16,093	35,061	32,756
Amortization Expenses	776	810	1,491	1,345
Gross Voyage Profit (excluding Depreciation Expense)	$ 4,351	$ 2,250	$ 8,396	$ 4,609
Gross Voyage Profit Margin Percentage (in hundredths)	19.00%	12.00%	19.00%	12.00%
Dry Bulk Carriers [Member]
Segment Reporting Information [Line Items]
Fixed Revenue	$ 1,866	$ 1,758	$ 3,734	$ 3,284
Variable Revenue	1,113	3,505	2,368	7,094
Total Revenues	2,979	5,263	6,102	10,378
Voyage Expenses	1,936	3,380	4,516	6,946
Amortization Expenses	60	32	121	109
Loss (Income) of Unconsolidated Entities	(208)	89	(843)	169
Gross Voyage Profit (excluding Depreciation Expense)	$ 1,191	$ 1,762	$ 2,308	$ 3,154
Gross Voyage Profit Margin Percentage (in hundredths)	40.00%	33.00%	38.00%	30.00%
Rail-Ferry [Member]
Segment Reporting Information [Line Items]
Variable Revenue	$ 9,827	$ 9,739	$ 17,612	$ 17,667
Total Revenues	9,827	9,739	17,612	17,667
Voyage Expenses	7,590	7,577	14,476	14,423
Amortization Expenses	136	256	421	416
Loss (Income) of Unconsolidated Entities	(117)	39	(43)	67
Gross Voyage Profit (excluding Depreciation Expense)	$ 2,218	$ 1,867	$ 2,758	$ 2,761
Gross Voyage Profit Margin Percentage (in hundredths)	23.00%	19.00%	16.00%	16.00%
Specialty Contracts [Member]
Segment Reporting Information [Line Items]
Fixed Revenue	$ 11,073	$ 8,487	$ 21,644	$ 17,188
Variable Revenue	647	911	832	3,158
Total Revenues	11,720	9,398	22,476	20,346
Voyage Expenses	9,662	7,736	17,219	17,212
Amortization Expenses	262	710	560	1,434
Loss (Income) of Unconsolidated Entities	(340)	(48)	(672)	(48)
Gross Voyage Profit (excluding Depreciation Expense)	$ 2,136	$ 1,000	$ 5,369	$ 1,748
Gross Voyage Profit Margin Percentage (in hundredths)	18.00%	11.00%	24.00%	9.00%
Other [Member]
Segment Reporting Information [Line Items]
Variable Revenue	$ 64	$ (17)	$ 51	$ 30
Total Revenues	64	(17)	51	30
Voyage Expenses	(122)	(487)	(544)	(814)
Gross Voyage Profit (excluding Depreciation Expense)	$ 186	$ 470	$ 595	$ 844

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 FASB

-Name Accounting Standards Codification

-Topic 323

-SubTopic 10

-Section 45

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=35755396&loc=d3e33749-111570

Reference 3: 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 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 9

-Article 5

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

- 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

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

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=ish_JonesActMember
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:

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=ish_DryBulkCarriersMember
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: