Property, Plant and Equipment (Details) (USD $)	Jun. 30, 2012	Dec. 31, 2011
Property, plant and equipment
Land and land improvements	$ 4,974,000	$ 4,974,000
Buildings	41,447,000	41,433,000
Machinery and equipment	227,920,000	224,426,000
Construction-in-progress	14,887,000	12,446,000
Other	8,431,000	8,419,000
Property, plant and equipment, Gross	297,659,000	291,698,000
Accumulated depreciation	(147,051,000)	(141,458,000)
Property, plant and equipment, Net	$ 150,607,833	$ 150,239,845