Recently Adopted Accounting Pronouncements - Schedule of Effects of ASC 606 (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Jan. 01, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Accounts receivable	$ 13,072,691		$ 13,072,691			$ 17,246,540
Other current assets	2,540,427		2,540,427		$ 1,581,535	785,027
Unearned charter hire revenue	4,901,453		4,901,453		7,262,291	5,678,673
Income Statement [Abstract]
Revenues, net	74,938,700	$ 53,631,224	154,309,309	$ 99,486,281
Voyage expenses	17,204,964	13,379,664	39,719,556	26,733,011
Charter hire expenses	10,108,258	6,445,580	20,376,322	10,318,912
Net income/(loss)	$ 3,450,767	$ (5,888,466)	$ 3,503,512	$ (16,956,914)
Basic income per share (in dollars per share)	$ 0.05	$ (0.08)	$ 0.05	$ (0.25)
Diluted income per share (in dollars per share)	$ 0.05	$ (0.08)	$ 0.05	$ (0.25)
Accumulated deficit	$ (424,448,411)		$ (424,448,411)		(427,951,923)	(427,164,813)
Calculated under Revenue Guidance in Effect before Topic 606
Statement of Financial Position [Abstract]
Accounts receivable	13,982,571		13,982,571
Other current assets	2,178,304		2,178,304			785,027
Unearned charter hire revenue	4,709,434		4,709,434			5,678,673
Income Statement [Abstract]
Revenues, net	75,293,766		153,827,542
Voyage expenses	17,236,431		39,505,136
Charter hire expenses	10,128,774		20,161,169
Net income/(loss)	$ 3,753,850		$ 3,451,318
Basic income per share (in dollars per share)	$ 0.05		$ 0.05
Diluted income per share (in dollars per share)	$ 0.05		$ 0.05
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	$ (909,880)		$ (909,880)
Other current assets	362,123		362,123		796,508
Unearned charter hire revenue	192,019		192,019		1,583,618
Income Statement [Abstract]
Revenues, net	(355,066)		481,767
Voyage expenses	31,467		(214,420)
Charter hire expenses	20,516		(215,153)
Net income/(loss)	$ (303,083)		$ 52,194
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)