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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The amount of expense recognized in the current period that reflects the allocation of the cost of tangible assets over the assets' useful lives. Includes production and non-production related depreciation.

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- Definition

Gross amount, at the balance sheet date, of long-lived physical assets used in the normal conduct of business and not intended for resale. This can include land, buildings, machinery and equipment, and other types of furniture and equipment including, but not limited to, office equipment, furniture and fixtures, and computer equipment and software.

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- Definition

Tangible assets that are held by an entity for use in the production or supply of goods and services, for rental to others, or for administrative purposes and that are expected to provide economic benefit for more than one year; net of accumulated depreciation. Examples include land, buildings, machinery and equipment, and other types of furniture and equipment including, but not limited to, office equipment, furniture and fixtures, and computer equipment and software.

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Property, Plant and Equipment (Details) (USD $)	3 Months Ended		6 Months Ended
Property, Plant and Equipment (Details) (USD $)	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Mar. 31, 2012
Property, Plant and Equipment [Line Items]
Property, plant, and equipment costs	$ 1,877,718,000		$ 1,877,718,000		$ 1,818,550,000
Accumulated depreciation	1,340,991,000		1,340,991,000		1,301,939,000
Property, plant and equipment, net	536,727,000		536,727,000		516,611,000
Depreciation expense	22,400,000	22,000,000	43,100,000	44,000,000
Land [Member]
Property, Plant and Equipment [Line Items]
Property, plant, and equipment costs	47,102,000		47,102,000		46,529,000
Buildings and building improvements [Member]
Property, Plant and Equipment [Line Items]
Property, plant, and equipment costs	394,548,000		394,548,000		374,042,000
Machinery and equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant, and equipment costs	1,360,983,000		1,360,983,000		1,314,303,000
Projects in progress [Member]
Property, Plant and Equipment [Line Items]
Property, plant, and equipment costs	$ 75,085,000		$ 75,085,000		$ 83,676,000