Dispositions - Additional Information (Detail) (USD $)	9 Months Ended		9 Months Ended		1 Months Ended	3 Months Ended	9 Months Ended
	Sep. 30, 2012	Dec. 31, 2011	Sep. 30, 2012 Charter Fleet Business Vessel	Sep. 30, 2012 Secunda International Limited Vessel	Aug. 26, 2011 DB 23marine vessel	Sep. 30, 2011 DB 23marine vessel	Sep. 30, 2011 DB 23marine vessel	Sep. 30, 2012 Multi Function Support Vessel Vessel
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of vessels held for sale								3
Assets held for sale, other current assets	$ 2,700,000	$ 3,197,000
Assets held for sale, long-term assets	28,724,000	55,571,000
Assets held for sale	31,400,000
Proceeds from sale of business			61,000,000		8,000,000
Gain on disposal of discontinued operations	$ 257,000		$ 257,000			$ 7,700,000	$ 7,700,000
Number of vessels			10	14