Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Consolidated Balance Sheets
Accounts and notes receivable, allowance for doubtful accounts	$ 3,128	$ 2,001
Accumulated depreciation	$ 404,549	$ 404,141
Ordinary shares, nominal value	$ 0.01	$ 0.01
Ordinary shares, shares issued	46,105,014	45,696,338
Ordinary shares, shares outstanding	46,105,014	45,696,338