Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Condensed Consolidated Balance Sheets [Abstract]
Allowance for doubtful accounts	$ 13,217	$ 12,080
Accumulated depreciation and depletion on Property, plant and equipment	2,618,764	2,640,344
Accumulated amortization of Intangible and other long-term assets	$ 23,037	$ 76,358
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	250,000,000	250,000,000
Common stock, shares issued	156,573,160	154,885,418
Common stock, shares outstanding	156,573,160	154,885,418