Property, Plant and Equipment (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014	Sep. 30, 2014
Components of property, plant and equipment
Land	$ 30,285	$ 23,380	$ 22,415
Land improvements and leasehold improvements	76,414	71,817	68,976
Buildings and storage facilities	301,125	275,059	238,664
Machinery and equipment	368,338	333,559	320,648
Software	70,781	55,436	55,791
Construction in progress	21,044	29,620	28,260
Property, plant and equipment, gross	867,987	788,871	734,754
Less: accumulated depreciation and amortization	372,942	335,264	332,954
Property, plant and equipment, net	$ 495,045	$ 453,607	$ 401,800