Leases (Tables)
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12 Months Ended | 
Dec. 31, 2021  | 
| Leases [Abstract] | 
 
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| Lease Assets and Liabilities | 
 Total lease assets and liabilities as of December 31, 2021 and 2020 were as follows:  
  
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| Lease Assets | 
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Classification  | 
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December 31, 2021 | 
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December 31, 2020 | 
 
| Operating lease right-of-use assets | 
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Operating lease right-of-use assets | 
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$ | 
148,198  | 
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$ | 
123,338  | 
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| Finance lease assets | 
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Property and equipment, net1  | 
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13,797  | 
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6,642  | 
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Total leased assets | 
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$ | 
161,995  | 
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$ | 
129,980  | 
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| Lease Liabilities  | 
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Classification | 
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December 31, 2021 | 
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December 31, 2020 | 
 
| Current:  | 
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|     Operating   | 
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Current portion of operating lease liabilities | 
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$ | 
47,532  | 
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$ | 
43,680  | 
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|      Finance | 
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Current portion of debt and finance lease obligations | 
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4,588  | 
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1,801  | 
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| Noncurrent:  | 
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|    Operating | 
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Operating lease liabilities, less current portion  | 
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101,409  | 
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80,346  | 
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|     Finance | 
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Finance lease obligations, less current portion  | 
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9,571  | 
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5,010  | 
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Total leased liabilities | 
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$ | 
163,100  | 
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$ | 
130,837  | 
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1 Finance lease assets are recorded net of accumulated depreciation of $4,822 and $2,256 as of December 31, 2021 and 2020, respectively. 
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| Lease Costs | 
 Total lease cost for 2021 and 2020 was as follows:  
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Year Ended | 
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Classification | 
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December 31, 2021 | 
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December 31, 2020 | 
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| Operating lease cost | 
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Operating leases  | 
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$ | 
54,561  | 
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$ | 
50,561  | 
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| Short-term lease cost | 
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Operating leases | 
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14,773  | 
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8,921  | 
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| Variable lease cost | 
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Purchased transportation, operating leases and other operating expenses | 
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367,779  | 
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339,148  | 
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| Sublease income | 
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Operating revenue | 
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(2,050) | 
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(1,628) | 
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| Finance lease cost: | 
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| Amortization of leased assets | 
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Depreciation and amortization | 
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3,381  | 
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1,560  | 
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| Interest on leased liabilities | 
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Interest expense, net | 
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301  | 
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197  | 
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| Total lease cost | 
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$ | 
438,745  | 
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$ | 
398,759  | 
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The following table summarizes the weighted-average remaining lease term and weighted average discount rate:  
  
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December 31, 2021 | 
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December 31, 2020 | 
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| Weighted average remaining lease term (in years):  | 
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|       Operating leases | 
4.1 | 
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3.7 | 
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|        Finance leases  | 
3.5 | 
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4.0 | 
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| Weighted average discount rate:  | 
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|        Operating leases | 
2.9  | 
% | 
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3.2  | 
% | 
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|         Finance leases  | 
2.6  | 
% | 
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3.1  | 
% | 
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The following table summarizes the supplemental cash flow information for 2021 and 2020: 
  
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Year Ended  | 
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December 31, 2021 | 
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December 31, 2020 | 
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| Cash paid for amounts included in the measurement of lease liabilities: | 
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| Operating cash flows from operating leases | 
$ | 
53,981  | 
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$ | 
50,263  | 
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| Operating cash flows from finance leases | 
301  | 
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197  | 
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| Financing cash flows from finance leases | 
2,423  | 
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1,446  | 
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| Right-of-use assets obtained in exchange for operating lease liabilities | 
$ | 
74,736  | 
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$ | 
72,454  | 
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| Leased assets obtained in exchange for finance lease obligations | 
9,673  | 
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1,927  | 
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| Aggregate Future Minimum Lease Payments Under Noncancelable Operating Leases | 
 Future minimum lease payments under noncancelable operating and finance leases with remaining terms greater than one year as of December 31, 2021 were as follows: 
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Operating Leases | 
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Finance Leases | 
 
| 2022 | 
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$ | 
52,832  | 
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$ | 
4,902  | 
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| 2023 | 
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39,558  | 
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4,468  | 
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| 2024 | 
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31,029  | 
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3,545  | 
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| 2025 | 
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20,261  | 
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1,331  | 
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| 2026 | 
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12,371  | 
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313  | 
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| Thereafter | 
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15,745  | 
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449  | 
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| Total minimum lease payments | 
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171,796  | 
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15,008  | 
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| Less: imputed interest | 
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(22,855) | 
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(849) | 
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| Present value of future minimum lease payments | 
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148,941  | 
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14,159  | 
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| Less: current portion of lease obligations | 
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(47,532) | 
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(4,588) | 
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| Long-term lease obligations | 
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$ | 
101,409  | 
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$ | 
9,571  | 
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| Aggregate Future Minimum Lease Payments Under Noncancelable Finance Leases | 
 Future minimum lease payments under noncancelable operating and finance leases with remaining terms greater than one year as of December 31, 2021 were as follows: 
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Operating Leases | 
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Finance Leases | 
 
| 2022 | 
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$ | 
52,832  | 
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$ | 
4,902  | 
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| 2023 | 
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39,558  | 
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4,468  | 
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| 2024 | 
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31,029  | 
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3,545  | 
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| 2025 | 
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20,261  | 
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1,331  | 
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| 2026 | 
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12,371  | 
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313  | 
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| Thereafter | 
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15,745  | 
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449  | 
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| Total minimum lease payments | 
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171,796  | 
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15,008  | 
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| Less: imputed interest | 
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(22,855) | 
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(849) | 
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| Present value of future minimum lease payments | 
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148,941  | 
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14,159  | 
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| Less: current portion of lease obligations | 
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(47,532) | 
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(4,588) | 
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| Long-term lease obligations | 
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$ | 
101,409  | 
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$ | 
9,571  | 
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