Consolidated Statements of Comprehensive Income (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Income Statement [Abstract]
Operating Revenue	$ 217,092	$ 130,645	$ 668,358	$ 398,909
Operating Expenses
Salaries, wages, and benefits	68,688	39,556	210,872	121,093
Rent and purchased transportation	12,518	1,112	40,770	3,735
Fuel	53,435	39,261	175,998	120,876
Operations and maintenance	9,977	4,987	29,874	14,256
Operating taxes and licenses	5,189	1,972	15,354	6,856
Insurance and claims	5,155	2,016	16,621	9,620
Communications and utilities	1,564	767	4,947	2,239
Depreciation and amortization	27,754	15,117	78,996	47,112
Other operating expenses	7,779	4,334	24,465	11,839
Gain on disposal of property and equipment	(11,257)	(4,477)	(27,160)	(24,299)
Total operating expenses	180,802	104,645	570,737	313,327
Operating income	36,290	26,000	97,621	85,582
Interest income	21	126	163	378
Interest expense	(97)	0	(384)	0
Income before income taxes	36,214	26,126	97,400	85,960
Federal and state income taxes	13,477	10,258	34,111	31,220
Net income	22,737	15,868	63,289	54,740
Other comprehensive income, net of tax	0	454	0	1,054
Comprehensive income	$ 22,737	$ 16,322	$ 63,289	$ 55,794
Net income per share
Basic	$ 0.26	$ 0.19	$ 0.72	$ 0.65
Diluted	$ 0.26	$ 0.19	$ 0.72	$ 0.64
Weighted average shares outstanding
Basic	87,778	84,837	87,737	84,799
Diluted	87,923	85,038	87,921	85,041
Dividends declared per share	$ 0.02	$ 0.02	$ 0.06	$ 0.06