Acquisitions (Business Acquisition, Pro Forma Information) (Details) (United Ocean Services, LLC [Member], USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
United Ocean Services, LLC [Member]
Business Acquisition [Line Items]
Revenues	$ 329,079	$ 385,938
Net earnings attributable to ISH	$ 30,765	$ 39,166
Basic (in dollars per share)	$ 4.28	$ 5.49
Diluted (in dollars per share)	$ 4.27	$ 5.46