Quarterly Financial Information (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Quarterly Financial Information [Abstract]
Revenues	$ 76,193	$ 77,938	$ 74,897	$ 81,124	$ 56,810	$ 61,162	$ 60,320	$ 65,204	$ 310,152	$ 243,496	$ 263,196
Voyage Expenses	57,392	64,832	61,508	69,591	45,262	45,394	47,026	50,826	247,622	185,453	190,150
Operating Income	5,978	1,959	1,404	306	10,128	4,013	3,518	6,312	9,647	23,971	43,609
Net Income (Loss)	$ 16,868	$ (2,222)	$ 1,859	$ 1,653	$ 11,540	$ 1,782	$ 704	$ 7,936	$ 18,157	$ 21,962	$ 31,549
Basic and Diluted Earnings per Common Share:
Basic Earnings Per Common Share: (in dollars per share)	$ 2.15	$ (0.46)	$ 0.17	$ 0.19	$ 1.60	$ 0.25	$ 0.10	$ 1.11	$ 2.06	$ 3.05	$ 4.42
Diluted Earnings Per Common Share: (in dollars per share)	$ 2.13	$ (0.46)	$ 0.17	$ 0.19	$ 1.60	$ 0.25	$ 0.10	$ 1.11	$ 2.05	$ 3.04	$ 4.40