Changes in Accounting Estimate (Details) (USD $)	6 Months Ended
	Jun. 30, 2012
Changes in Accounting Estimate [Abstract]
Period between salvage value reviews	3 years
Period used to determine reasonableness of salvage values	3 years
Change in Salvage Value [Member]
Change in Accounting Estimate [Line Items]
Number of vessels for which salvage values were adjusted	8
Decrease in Future Depreciation Expense	$ 3,800,000
Increase in pre-tax income	1,890,000
Increase in net income	$ 1,890,000
Increase in Basic Earnings per Share	$ 0.26
Increase in diluted earnings per share (in dollars per share)	$ 0.26