Property, Plant and Equipment (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016	Mar. 31, 2016
Components of property, plant and equipment
Land	$ 29,331	$ 30,672	$ 30,138
Land improvements and leasehold improvements	78,798	79,631	77,531
Buildings and storage facilities	321,344	322,856	304,276
Machinery and equipment	388,230	392,418	377,879
Construction in progress	13,113	12,784	47,755
Property, plant and equipment, gross	830,816	838,361	837,579
Less: accumulated depreciation	390,421	388,309	374,918
Property, plant and equipment, net	$ 440,395	$ 450,052	$ 462,661