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Property, plant and equipment
 12 Months Ended
Dec. 31, 2020
Property, Plant and Equipment [Abstract]  
Property, plant and equipment Property, plant and equipment
December 31, 2020CostAccumulated
Depreciation		Net Book Value
Owned assets
Heavy equipment$352,948 $102,624 $250,324 
Major component parts in use326,022 111,583 214,439 
Other equipment41,934 27,041 14,893 
Licensed motor vehicles16,387 10,592 5,795 
Office and computer equipment6,337 4,137 2,200 
Land10,472 — 10,472 
Buildings22,701 3,062 19,639 
776,801 259,039 517,762 
Assets under finance lease
Heavy equipment97,871 25,454 72,417 
Major component parts in use52,798 16,264 36,534 
Other equipment5,287 966 4,321 
Licensed motor vehicles3,629 959 2,670 
159,585 43,643 115,942 
Total property, plant and equipment$936,386 $302,682 $633,704 
December 31, 2019CostAccumulated
Depreciation		Net Book Value
Owned assets
Heavy equipment$299,298 $70,031 $229,267 
Major component parts in use252,328 92,161 160,167 
Other equipment40,344 25,328 15,016 
Licensed motor vehicles14,270 9,463 4,807 
Office and computer equipment5,154 3,511 1,643 
Land13,829 — 13,829 
Buildings26,281 2,421 23,860 
651,504 202,915 448,589 
Assets under finance lease
Heavy equipment132,270 43,466 88,804 
Major component parts in use71,706 27,918 43,788 
Other equipment2,126 264 1,862 
Licensed motor vehicles5,617 1,551 4,066 
Office and computer equipment691 71 620 
212,410 73,270 139,140 
Total property, plant and equipment$863,914 $276,185 $587,729