Property, Plant and Equipment (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017
Components of property, plant and equipment
Land	$ 29,915	$ 22,388	$ 29,331
Land improvements and leasehold improvements	69,320	69,127	78,798
Buildings and storage facilities	285,084	284,820	321,344
Machinery and equipment	377,563	373,127	388,230
Construction in progress	15,116	7,502	13,113
Property, plant and equipment, gross	776,998	756,964	830,816
Less: accumulated depreciation	383,235	372,287	390,421
Property, plant and equipment, net	$ 393,763	$ 384,677	$ 440,395