Property, Plant and Equipment (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Property, plant and equipment
Property, plant and equipment, Gross	$ 257,214	$ 256,487
Accumulated depreciation	(198,828)	(195,795)
Total property, plant and equipment, net	58,386	60,692
Manufacturing equipment [Member]
Property, plant and equipment
Property, plant and equipment, Gross	174,588	174,353
Land [Member]
Property, plant and equipment
Property, plant and equipment, Gross	8,101	8,101
Buildings and improvements [Member]
Property, plant and equipment
Property, plant and equipment, Gross	54,081	53,792
Office furniture and research equipment [Member]
Property, plant and equipment
Property, plant and equipment, Gross	$ 20,444	$ 20,241

The cumulative amount of depreciation, depletion and amortization (related to property, plant and equipment, but not including land) that has been recognized in the income statement.

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Gross amount of long-lived physical assets used in the normal conduct of business and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment.

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- Definition

Amount, net of accumulated depreciation, depletion and amortization, of long-lived physical assets used in the normal conduct of business and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment.

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