Plant Closure (Details) (USD $)				3 Months Ended	6 Months Ended	12 Months Ended		6 Months Ended
	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2012	Mar. 31, 2013 Facility closing	Jun. 30, 2013 Facility closing	Dec. 31, 2012 Facility closing	Dec. 31, 2012 Facility closing Land and building	Jun. 30, 2013 Facility closing Operating expenses
Plant Closure
Net book value of the long-lived assets, including land, building and equipment	$ 209,544,000	$ 213,452,000	$ 208,685,000			$ 2,800,000	$ 2,700,000
Impairment loss on assets held and in use				1,000,000
Net book value of remaining equipments to be sold, transferred or scrapped	586,000	593,000			100,000
Severance costs					0	3,000,000
Severance costs paid					77,000	2,400,000
Severance costs reversed					36,000
Severance costs accrued						600,000
Severance costs to be paid in 2013					400,000
Estimated closure costs					400,000			700,000
Plant closure expenses					35,000	300,000
Plant closure expenses paid					125,000	200,000
Plant closure expenses to be paid in 2013					$ 18,000	$ 100,000