Acquisitions - Narrative (Details)
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12 Months Ended |
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Jun. 01, 2015
USD ($)
Employee_grantedoptions
granttoseller
shares
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Feb. 01, 2015
USD ($)
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Dec. 31, 2017
USD ($)
shares
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Dec. 31, 2016
USD ($)
shares
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Dec. 31, 2015
USD ($)
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| Business Acquisition [Line Items] |
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| Change in contingent consideration due to seller |
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$ (1,069,533)
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$ 112,954
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$ (201,452)
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| Performance Shares |
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| Business Acquisition [Line Items] |
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| Granted (in shares) | shares |
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27,185
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24,064
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| Stock-based compensation expense |
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$ 405,700
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$ 235,880
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595,870
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| Restricted Stock |
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| Business Acquisition [Line Items] |
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| Granted (in shares) | shares |
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268,300
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284,086
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| Number of shares outstanding | shares |
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521,340
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559,491
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| Stock-based compensation expense |
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$ 5,731,731
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$ 10,625,440
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11,821,382
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| Xpress Solutions |
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| Business Acquisition [Line Items] |
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| Payments to acquire the business in cash |
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$ 6,054,937
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| Additional contingent consideration |
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$ 3,000,000
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| Change in contingent consideration due to seller |
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(1,049,533)
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192,091
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| Contingent consideration liability |
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$ 1,700,000
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$ 970,000
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| Command Transportation, LLC |
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| Business Acquisition [Line Items] |
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| Payments to acquire the business in cash |
$ 394,279,778
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| Fair value of total consideration transferred |
$ 407,706,392
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| Command Transportation, LLC | Management |
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| Business Acquisition [Line Items] |
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| Number of employees granted shares | granttoseller |
2
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| Command Transportation, LLC | Performance Shares | Management |
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| Business Acquisition [Line Items] |
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| Granted (in shares) | shares |
67,178
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| Number of shares outstanding | shares |
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0
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33,589
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| Command Transportation, LLC | Restricted Stock |
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| Business Acquisition [Line Items] |
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| Granted (in shares) | shares |
335,882
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| Number of employees granted shares | Employee_grantedoptions |
33
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| Command Transportation, LLC | Restricted Stock | Management |
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| Business Acquisition [Line Items] |
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| Granted (in shares) | shares |
100,766
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| Number of shares outstanding | shares |
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0
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33,588
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| Stock-based compensation expense |
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$ 400,000
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$ 5,300,000
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$ 7,300,000
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