Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Current assets:
Allowance for doubtful accounts	$ 52,072	$ 51,920
Accumulated depreciation on property, plant and equipment	$ 911,160	$ 882,151
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	46,575,000	46,980,000