Leases (Details Textual) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015
Charters In [Member]
Leases [Line Items]
Commitments to charter in vessels, Number of Units	17
Bareboat Charters In [Member]
Leases [Line Items]
Commitments to charter in vessels, Number of Units	13
Charter Out [Member]
Leases [Line Items]
Operating Leases, Future Minimum Payments Receivable, Current	324,838
Operating Leases, Future Minimum Payments Receivable, in Two Years	283,393
Operating Leases, Future Minimum Payments Receivable, in Three Years	178,914
Operating Leases, Future Minimum Payments Receivable, in Four Years	123,156
Operating Leases, Future Minimum Payments Receivable, in Five Years	78,067
Operating Leases, Future Minimum Payments Receivable, Thereafter	176,082
Charter Out [Member] | Contract of Affreightmen [Member]
Leases [Line Items]
Operating Leases, Future Minimum Payments Receivable, Current	19,373
Operating Leases, Future Minimum Payments Receivable, in Two Years	22,023
Operating Leases, Future Minimum Payments Receivable, in Three Years	22,347
Operating Leases, Future Minimum Payments Receivable, in Four Years	22,698
Operating Leases, Future Minimum Payments Receivable, in Five Years	23,031
Operating Leases, Future Minimum Payments Receivable, Thereafter	6,356