Vessel Acquisitions and Dispositions (Details) (North Sea [Member], USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2012 ft DWT hp
Remontowa [Member] | Large Platform Supply Vessel One [Member]
New build program
Expected Delivery	Q2 2013
Length (feet)	291
Breakhorse Power	9,120
Deadweight Tons	5,100
Expected Cost	$ 41.0
Remontowa [Member] | Large Platform Supply Vessel Two [Member]
New build program
Expected Delivery	Q3 2013
Length (feet)	291
Breakhorse Power	9,120
Deadweight Tons	5,100
Expected Cost	41.1
Remontowa [Member] | Large Platform Supply Vessel Three [Member]
New build program
Expected Delivery	Q3 2013
Length (feet)	260
Breakhorse Power	9,120
Deadweight Tons	4,000
Expected Cost	37.7
Rosetti Marino [Member] | Large Platform Supply Vessel Four [Member]
New build program
Expected Delivery	Q4 2013
Length (feet)	246
Breakhorse Power	7,483
Deadweight Tons	3,000
Expected Cost	32.1
Rosetti Marino [Member] | Large Platform Supply Vessel Five [Member]
New build program
Expected Delivery	Q1 2014
Length (feet)	246
Breakhorse Power	7,483
Deadweight Tons	3,000
Expected Cost	32.1
Simek [Member] | Large Platform Supply Vessel Six [Member]
New build program
Expected Delivery	Q2 2013
Length (feet)	304
Breakhorse Power	11,265
Deadweight Tons	4,700
Expected Cost	60.9
Simek [Member] | Large Platform Supply Vessel Seven [Member]
New build program
Expected Delivery	Q4 2013
Length (feet)	304
Breakhorse Power	11,265
Deadweight Tons	4,700
Expected Cost	$ 60.9