Property, Plant and Equipment (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Components of property, plant and equipment
Land	$ 21,801	$ 22,258
Land improvements and leasehold improvements	67,153	63,013
Buildings and storage facilities	231,976	214,919
Machinery and equipment	308,215	287,896
Software	13,351	12,901
Construction in progress	48,135	34,965
Property, plant and equipment, gross	690,631	635,952
Less: accumulated depreciation and amortization	303,173	277,074
Property, plant and equipment, net	$ 387,458	$ 358,878