Condensed Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data	Jun. 30, 2011	Dec. 31, 2010
Current assets:
Allowance for doubtful accounts	$ 23,984	$ 22,618
Accumulated depreciation and depletion of property, plant and equipment	861,737	771,602
Accumulated amortization of intangible and other long-term assets	$ 26,228	$ 22,065
Stockholders' equity:
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, shares issued	0	0
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	125,000,000	125,000,000
Common stock, shares issued	79,822,534	78,951,053
Common stock, shares outstanding	79,822,534	78,951,053