Net Property, Plant and Equipment (Tables)

12 Months Ended

Dec. 31, 2014

Net Property, Plant and Equipment

Summary of property, plant and equipment

	Useful	December 31,
(Thousands of dollars)	Lives	2014			2013
Land and improvements	0-15 years	$	184,647		$	194,237
Buildings and improvements	30 years	389,193			395,598
Machinery and equipment	3-20 years	1,001,061			990,553
Vessels and vehicles	3-18 years	160,310			126,502
Office furniture and fixtures	5 years	25,965			30,102
Construction in progress		25,535			40,317
		1,786,711			1,777,309
Accumulated depreciation and amortization		(939,954		)	(913,736		)
Net property, plant and equipment		$	846,757		$	863,573