Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Current assets:
Allowance for doubtful accounts	$ 66,252	$ 53,412
Contract asset, allowance for doubtful accounts	2,681
Accumulated depreciation on property, plant and equipment	1,007,261	1,013,207
Other assets, allowance for credit loss	$ 100,887	$ 101,439
Shareholders’ equity:
Common shares, par value (in dollars per share)	$ 1.25	$ 1.25
Common shares, shares authorized (in shares)	305,000,000	305,000,000
Common shares, shares issued (in shares)	176,793,000	176,793,000
Treasury shares, shares (in shares)	47,002,000	46,262,000