Recent Accounting Pronouncements - Schedule of Effects of ASC 606 (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Jan. 01, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Accounts receivable	$ 16,142,605		$ 16,142,605			$ 17,246,540
Other current assets	2,693,532		2,693,532		$ 1,581,535	785,027
Unearned charter hire revenue	5,974,568		5,974,568		7,262,291	5,678,673
Income Statement [Abstract]
Revenues, net	69,092,740	$ 62,710,903	223,402,049	$ 162,197,184
Voyage expenses	15,126,287	17,462,699	54,845,843	44,195,710
Charter hire expenses	7,459,921	9,652,468	27,836,243	19,971,380
Net income/(loss)	$ 2,584,822	$ (10,255,346)	$ 6,088,334	$ (27,212,260)
Basic income per share (in dollars per share)	$ 0.04	$ (0.15)	$ 0.09	$ (0.40)
Diluted income per share (in dollars per share)	$ 0.04	$ (0.15)	$ 0.08	$ (0.40)
Accumulated deficit	$ (421,863,589)		$ (421,863,589)		(427,951,923)	(427,164,813)
Calculated under Revenue Guidance in Effect before Topic 606
Statement of Financial Position [Abstract]
Accounts receivable	16,959,548		16,959,548
Other current assets	2,289,473		2,289,473			785,027
Unearned charter hire revenue	5,751,495		5,751,495			5,678,673
Income Statement [Abstract]
Revenues, net	69,030,905		222,858,447
Voyage expenses	15,141,151		54,646,287
Charter hire expenses	7,453,073		27,614,242
Net income/(loss)	$ 2,514,971		5,966,289
Basic income per share (in dollars per share)	$ 0.04
Diluted income per share (in dollars per share)	$ 0.03
Accumulated deficit						$ (427,164,813)
Calculated under Revenue Guidance in Effect before Topic 606 | Bunker Expenses
Statement of Financial Position [Abstract]
Other current assets					600,000
Calculated under Revenue Guidance in Effect before Topic 606 | Charter Hire Expenses
Statement of Financial Position [Abstract]
Other current assets					200,000
Calculated under Revenue Guidance in Effect before Topic 606 | Voyage In Progress
Statement of Financial Position [Abstract]
Unearned charter hire revenue					1,500,000
Accounting Standards Update 2014-09 | Difference between Revenue Guidance in Effect before and after Topic 606
Statement of Financial Position [Abstract]
Accounts receivable	$ (816,943)		(816,943)
Other current assets	404,059		404,059		796,508
Unearned charter hire revenue	223,073		223,073		1,583,618
Income Statement [Abstract]
Revenues, net	61,835		543,602
Voyage expenses	14,864		(199,556)
Charter hire expenses	(6,848)		(222,001)
Net income/(loss)	$ 69,851		$ 122,045
Basic income per share (in dollars per share)	$ 0.00		$ 0.00
Diluted income per share (in dollars per share)	$ 0.00		$ 0.00
Accumulated deficit					$ (787,110)