Consolidated Statements of Operations (Unaudited) - USD ($)
3 Months Ended 9 Months Ended
Sep. 30, 2016
Sep. 30, 2015
Sep. 30, 2016
Sep. 30, 2015
Income Statement [Abstract]        
Revenue $ 460,191,903 $ 449,993,415 $ 1,309,299,359 $ 1,105,127,231
Costs and expenses:        
Transportation costs 379,329,380 362,614,918 1,062,432,444 894,955,721
Selling, general and administrative expenses 66,292,712 71,318,890 206,302,091 176,796,987
Depreciation and amortization 8,543,002 7,448,076 23,670,711 16,572,233
Income from operations 6,026,809 8,611,531 16,894,113 16,802,290
Interest income 0 0 0 23,909
Interest expense (3,565,093) (3,414,826) (10,592,654) (7,803,050)
Other expense 0 0 0 (126,295)
Interest and other expense (3,565,093) (3,414,826) (10,592,654) (7,905,436)
Income before provision for income taxes 2,461,716 5,196,705 6,301,459 8,896,854
Income tax expense (99,666) (1,738,000) (1,746,029) (2,792,000)
Net income $ 2,362,050 $ 3,458,705 $ 4,555,430 $ 6,104,854
Earnings per common share:        
Basic (in usd per share) $ 0.08 $ 0.12 $ 0.16 $ 0.23
Diluted (in usd per share) $ 0.08 $ 0.11 $ 0.15 $ 0.22