Property, Plant and Equipment (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012
Components of property, plant and equipment
Land	$ 23,348	$ 22,258	$ 19,699
Land improvements and leasehold improvements	67,262	63,013	59,375
Buildings and storage facilities	224,913	214,919	178,354
Machinery and equipment	299,874	287,896	257,926
Software	13,558	12,901	12,632
Construction in progress	54,713	34,965	28,582
Property, plant and equipment, gross	683,668	635,952	556,568
Less accumulated depreciation and amortization	303,294	277,074	273,174
Property, plant and equipment, net	$ 380,374	$ 358,878	$ 283,394