Leases (Details) (USD $)	3 Months Ended	0 Months Ended				3 Months Ended
	Mar. 31, 2013	Nov. 27, 2012 BMO Harris Equipment Finance Company [Member]	Nov. 27, 2012 Capital Source Bank [Member]	Dec. 27, 2012 BB&T Equipment Finance [Member]	Feb. 22, 2012 Wells Fargo Bank Northwest [Member]	Mar. 31, 2013 U.S. Flag PCTC [Member]	Mar. 31, 2013 International Flag PCTC [Member]
Capital Leased Assets [Line Items]
Lease expiration date						Oct. 31, 2015	May 31, 2019
Additional extended period of lease term	8 years
Book value of leased asset	$ 16,400,000
Quarterly depreciation on vessel	225,355
Operating Leased Assets [Line Items]
Transaction generated gross proceeds	63,000,000	32,000,000	31,000,000	32,000,000	59,000,000
Repayment of debt from proceeds of sale and leaseback transaction	54,500,000
Lease term		7 years	6 years	6 years	10 years
Gain on this sale-leaseback		$ 8,000,000	$ 11,700,000		$ 14,900,000