Property, Plant and Equipment (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Components of property, plant and equipment
Land	$ 22,258	$ 17,655
Land improvements and leasehold improvements	63,013	47,958
Buildings and storage facilities	214,919	150,461
Machinery and equipment	287,896	191,833
Software	12,901	10,861
Construction in progress	34,965	13,006
Property, plant and equipment, gross	635,952	431,774
Less: accumulated depreciation and amortization	277,074	256,687
Property, plant and equipment, net	$ 358,878	$ 175,087