Quarterly report pursuant to Section 13 or 15(d)

CONSOLIDATED CONDENSED BALANCE SHEETS (Parenthetical)

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CONSOLIDATED CONDENSED BALANCE SHEETS (Parenthetical) - USD ($)
$ in Thousands
Jun. 30, 2016
Dec. 31, 2015
Statement of Financial Position [Abstract]    
Allowance for bad debts $ 8,192 $ 8,694
Accumulated depreciation and amortization on property, plant and equipment $ 1,360,990 $ 1,302,380