Consolidated Balance Sheet Parenthetical (USD $)	Sep. 30, 2012	Dec. 31, 2011
Allowance for Doubtful Accounts Receivable, Current	$ 4,525,000	$ 4,361,000
Property, Plant, and Equipment, Owned, Accumulated Depreciation	$ 821,572,000	$ 779,449,000
Preferred Stock, Par or Stated Value Per Share	$ 0.01	$ 0.01
Preferred Stock, Shares Authorized	4,500,000	4,500,000
Preferred Stock, Shares Issued	0	0
Preferred Stock, Shares Outstanding	0	0
Common Stock, Par or Stated Value Per Share	$ 0.01	$ 0.01
Common Stock, Shares Authorized	75,000,000	75,000,000
Common Stock, Shares, Issued	48,457,461	48,432,860
Common Stock, Shares, Outstanding	48,457,461	48,432,860