Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Consolidated Balance Sheets
Property, plant and equipment, accumulated depreciation (in dollars)	$ 2,109,478	$ 2,049,821
Preferred stock, authorized shares	10,000,000	10,000,000
Preferred stock, issued shares	0	0
Common stock, authorized shares	200,000,000	200,000,000
Common stock, issued shares	97,425,467	96,038,328
Common stock, outstanding shares	97,425,467	96,038,328