Subsequent Events - Additional Information (Detail) (Revolving Credit Agreement, USD $) In Millions, unless otherwise specified		1 Months Ended
Dec. 31, 2012	Jan. 31, 2013 Subsequent Event Deepwater Platform Supply Vessels Vessel
Subsequent Event [Line Items]
Amount borrowed under revolving credit facility	$ 40.0	$ 50.0
Number of deepwater PSVs acquired		2

Amount borrowed under the credit facility as of the balance sheet date.

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 19, 22

-Article 5

Name:	us-gaap_LineOfCreditFacilityAmountOutstanding
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant