Restatement of Previously Issued Financial Statements (Impact on Consolidated Statements of Operations) (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016		Jun. 30, 2015
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Revenues	[1]	$ 483,417	$ 517,623	$ 949,963		$ 1,006,457
Operating expenses:
Purchased transportation costs	[1]	315,661	345,425	623,700		672,802
Personnel and related benefits	[1]	71,690	66,103	140,039		129,067
Other operating expenses	[1]	85,661	77,010	159,534		148,222
Depreciation and amortization	[1]	9,179	7,434	18,388		14,241
Total operating expenses	[1]	482,191	495,972	941,661		964,332
Operating income	[1]	1,226	21,651	8,302		42,125
Interest expense	[1]	5,695	4,373	11,303		8,982
(Loss) income before provision for income taxes	[1]	(4,469)	17,278	(3,001)		33,143
(Benefit from) provision for income taxes	[1]	(1,730)	6,707	(1,162)		12,752
Net income available to common stockholders	[1]	$ (2,739)	$ 10,571	$ (1,839)	[2]	$ 20,391	[2]
(Loss) earnings per share:
Basic (in dollars per share)	[1]	$ (0.07)	$ 0.28	$ (0.05)		$ 0.54
Diluted (in dollars per share)	[1]	$ (0.07)	$ 0.27	$ (0.05)		$ 0.52
Weighted average common stock outstanding:
Basic (in shares)	[1]	38,319,000	38,170,000	38,302,000		38,091,000
Diluted (in shares)	[1]	38,319,000	39,524,000	38,302,000		39,425,000
As Previously Reported
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Revenues		$ 483,432	$ 517,930	$ 949,064		$ 1,006,900
Operating expenses:
Purchased transportation costs		317,455	346,073	625,929		674,564
Personnel and related benefits		71,556	65,794	139,157		127,849
Other operating expenses		76,261	67,286	145,676		132,031
Depreciation and amortization		9,531	7,535	19,067		14,412
Total operating expenses		474,803	486,688	929,829		948,856
Operating income		8,629	31,242	19,235		58,044
Interest expense		5,695	4,373	11,303		8,982
(Loss) income before provision for income taxes		2,934	26,869	7,932		49,062
(Benefit from) provision for income taxes		1,136	10,398	3,069		18,987
Net income available to common stockholders		$ 1,798	$ 16,471	$ 4,863		$ 30,075
(Loss) earnings per share:
Basic (in dollars per share)		$ 0.05	$ 0.43	$ 0.13		$ 0.79
Diluted (in dollars per share)		$ 0.05	$ 0.42	$ 0.13		$ 0.76
Weighted average common stock outstanding:
Basic (in shares)		38,319,000	38,170,000	38,302,000		38,090,000
Diluted (in shares)		38,368,000	39,524,000	38,371,000		39,432,000
Adjustments
Operating expenses:
Net income available to common stockholders				$ (6,702)		$ (9,684)
Adjustments | Receivables & Related Reserves
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Revenues		$ (15)	$ (307)	1,899		(443)
Operating expenses:
Purchased transportation costs		0	0	0		0
Personnel and related benefits		0	0	0		0
Other operating expenses		1,635	1,656	2,188		3,635
Depreciation and amortization		0	0	0		0
Total operating expenses		1,635	1,656	2,188		3,635
Operating income		(1,650)	(1,963)	(289)		(4,078)
Interest expense		0	0	0		0
(Loss) income before provision for income taxes		(1,650)	(1,963)	(289)		(4,078)
(Benefit from) provision for income taxes		0	0	0		0
Net income available to common stockholders		(1,650)	(1,963)	(289)		(4,078)
Adjustments | Unrecorded Charges & Contingent Liabilities
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Revenues		0	0	(1,000)		0
Operating expenses:
Purchased transportation costs		(1,794)	(648)	(2,229)		(1,762)
Personnel and related benefits		134	309	882		1,218
Other operating expenses		6,101	4,113	6,135		6,145
Depreciation and amortization		0	0	0		0
Total operating expenses		4,441	3,774	4,788		5,601
Operating income		(4,441)	(3,774)	(5,788)		(5,601)
Interest expense		0	0	0		0
(Loss) income before provision for income taxes		(4,441)	(3,774)	(5,788)		(5,601)
(Benefit from) provision for income taxes		0	0	0		0
Net income available to common stockholders		(4,441)	(3,774)	(5,788)		(5,601)
Adjustments | Insurance Reserves & Related Receivables
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Revenues		0	0	0		0
Operating expenses:
Purchased transportation costs		0	0	0		0
Personnel and related benefits		0	0	0		0
Other operating expenses		(494)	1,454	785		2,827
Depreciation and amortization		0	0	0		0
Total operating expenses		(494)	1,454	785		2,827
Operating income		494	(1,454)	(785)		(2,827)
Interest expense		0	0	0		0
(Loss) income before provision for income taxes		494	(1,454)	(785)		(2,827)
(Benefit from) provision for income taxes		0	0	0		0
Net income available to common stockholders		494	(1,454)	(785)		(2,827)
Adjustments | Capital Improvements & Aircraft Spare Parts
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Revenues		0	0	0		0
Operating expenses:
Purchased transportation costs		0	0	0		0
Personnel and related benefits		0	0	0		0
Other operating expenses		2,158	2,501	4,750		3,584
Depreciation and amortization		(352)	(101)	(679)		(171)
Total operating expenses		1,806	2,400	4,071		3,413
Operating income		(1,806)	(2,400)	(4,071)		(3,413)
Interest expense		0	0	0		0
(Loss) income before provision for income taxes		(1,806)	(2,400)	(4,071)		(3,413)
(Benefit from) provision for income taxes		0	0	0		0
Net income available to common stockholders		(1,806)	(2,400)	(4,071)		(3,413)
Adjustments | Income Taxes & Debt Reclassification
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Revenues		0	0	0		0
Operating expenses:
Purchased transportation costs		0	0	0		0
Personnel and related benefits		0	0	0		0
Other operating expenses		0	0	0		0
Depreciation and amortization		0	0	0		0
Total operating expenses		0	0	0		0
Operating income		0	0	0		0
Interest expense		0	0	0		0
(Loss) income before provision for income taxes		0	0	0		0
(Benefit from) provision for income taxes		(2,866)	(3,691)	(4,231)		(6,235)
Net income available to common stockholders		$ 2,866	$ 3,691	$ 4,231		$ 6,235

[1] See Note 13 “Restatement of Previously Issued Financial Statements

[2] See Note 13 “Restatement of Previously Issued Financial Statements.”