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Plant and equipment (Tables)

12 Months Ended

Dec. 31, 2014

Property, Plant and Equipment [Abstract]

Property, plant and equipment

Depreciation is calculated based on the cost, net of the estimated residual value, over the estimated useful life of the assets on the following bases and rates:



Assets		Basis		Rate
Heavy equipment		Straight-line		Operating hours
Major component parts in use		Straight-line		Operating hours
Other equipment		Straight-line		5 – 10 years
Licensed motor vehicles		Straight-line		5 – 10 years
Office and computer equipment		Straight-line		4 years
Buildings		Straight-line		10 years
Leasehold improvements		Straight-line		Over shorter of estimated useful life and lease term



December 31, 2014		Cost				Accumulated Deprecation				Net Book Value
Heavy equipment		$	142,052			$	42,292			$	99,760
Major component parts in use		112,645				55,895				56,750
Other equipment		41,739				18,758				22,981
Licensed motor vehicles		24,247				20,763				3,484
Office and computer equipment		9,355				8,216				1,139
Buildings		2,791				2,606				185
Assets under capital lease		101,606				25,007				76,599
		$	434,435			$	173,537			$	260,898



December 31, 2013		Cost				Accumulated Deprecation				Net Book Value
Heavy equipment		$	251,872			$	96,038			$	155,834
Major component parts in use		60,484				23,472				37,012
Other equipment		27,594				11,511				16,083
Licensed motor vehicles		25,911				22,474				3,437
Office and computer equipment		13,846				11,882				1,964
Buildings		4,691				2,650				2,041
Leasehold improvements		9,946				6,187				3,759
Assets under capital lease		72,627				14,782				57,845
		$	466,971			$	188,996			$	277,975