CONSOLIDATED BALANCE SHEETS (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Statement Of Financial Position [Abstract]
Accounts receivable, allowance for doubtful accounts	$ 6,491	$ 6,697
Property, plant and equipment, accumulated depreciation, depletion and amortization	$ 8,794,519	$ 8,138,587
Cumulative Preferred Stock, par	$ 100	$ 100
Cumulative Preferred Stock, authorized	400,000	400,000
Cumulative Preferred Stock, issued
Common Stock, par	$ 1.00	$ 1.00
Common Stock, authorized	450,000,000	450,000,000
Common Stock, issued	194,770,571	194,616,470
Treasury stock, shares of Common Stock	7,881,548	3,975,153