Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Current assets:
Allowance for doubtful accounts	$ 31,729	$ 25,469
Accumulated depreciation on property, plant and equipment	$ 844,655	$ 836,981
Shareholders’ equity:
Common shares, par value (in dollars per share)	$ 1.25	$ 1.25
Common shares, shares authorized	305,000,000	305,000,000
Common shares, shares issued	176,793,000	176,793,000
Treasury shares, shares	44,200,000	42,444,000