Condensed Consolidated Statements of Operations - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
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
Vessel expenses	19,568,961	20,110,123	61,224,734	57,374,444
Charter hire expenses	7,459,921	9,652,468	27,836,243	19,971,380
Depreciation and amortization	9,460,192	8,980,992	28,009,067	24,494,397
General and administrative expenses	8,882,790	8,620,938	27,692,259	24,989,738
Gain on sale of vessels	(235,695)	(202,487)	(340,768)	(2,100,386)
Total operating expenses	60,262,456	64,624,733	199,267,378	168,925,283
Operating income/(loss)	8,830,284	(1,913,830)	24,134,671	(6,728,099)
Interest expense	6,574,826	7,836,999	19,222,906	21,140,746
Interest income	(130,020)	(142,940)	(337,248)	(518,379)
Other expense /(income)	(199,344)	647,457	(839,321)	(138,206)
Total other expense, net	6,245,462	8,341,516	18,046,337	20,484,161
Net income/(loss)	$ 2,584,822	$ (10,255,346)	$ 6,088,334	$ (27,212,260)
Weighted average shares outstanding:
Basic (in shares)	70,649,556	70,329,252	70,539,951	68,782,517
Diluted (in shares)	72,356,655	70,329,252	71,855,683	68,782,517
Per share amounts:
Basic income/(loss) (in dollars per share)	$ 0.04	$ (0.15)	$ 0.09	$ (0.40)
Diluted income/(loss) (in dollars per share)	$ 0.04	$ (0.15)	$ 0.08	$ (0.40)