Property, Plant and Equipment (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017
Components of property, plant and equipment
Land	$ 29,545	$ 22,388	$ 23,342
Land improvements and leasehold improvements	68,859	69,127	71,559
Buildings and storage facilities	282,826	284,820	298,951
Machinery and equipment	380,109	373,127	384,422
Construction in progress	65,539	7,502	7,703
Property, plant and equipment, gross	826,878	756,964	785,977
Less: accumulated depreciation	392,373	372,287	366,629
Property, plant and equipment, net	$ 434,505	$ 384,677	$ 419,348