Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Condensed Consolidated Balance Sheets [Abstract]
Allowance for doubtful accounts	$ 11,891	$ 12,156
Accumulated depreciation and depletion on Property, plant and equipment	2,193,111	2,214,116
Accumulated amortization of Intangible and other long-term assets	$ 23,459	$ 23,199
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	25,000,000	25,000,000
Common stock, shares issued	15,798,428	15,689,463
Common stock, shares outstanding	14,826,016	14,717,051
Treasury Stock, Shares	972,412	972,412