Description of Business (Details) (USD $) In Millions, unless otherwise specified	1 Months Ended		3 Months Ended		6 Months Ended
	Feb. 29, 2012 item	Dec. 31, 2011 item	Jun. 30, 2012	Mar. 31, 2012	Jun. 30, 2012 item
Description of Business [Abstract]
Number of vessels owned					17
Ownership interest in SSAT (as a percent)			35.00%		35.00%
Number of terminal facilities on which SSAT provides terminal and stevedoring services to Matnav and numerous international carriers					6
Number of publicly traded companies to be created after separation		2
Number of businesses wherein assets are segregated under reorganization	2
Maximum ownership interest that may be owned by non-U.S. citizens (as a percent)					22.00%
Maximum period during which services are to be provided under Transition Services Agreement					24
Total cash outflows expected to be incurred in relation to separation					$ 165.4
Total capital distributions to A&B (A)					155.7
Separation costs (B)			5.8	2.5	8.3
Capitalized debt financing costs					1.9
Total cash outflow related to the Separation					165.9
Net distribution in relation to separation			4.3
Separation costs, net of tax			$ 4.8	$ 2.1