Consolidated Condensed Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Allowance for doubtful trade accounts receivable	$ 9,233	$ 8,686
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	200,000,000	200,000,000
Common stock, shares issued	80,533,536	80,533,536
Common stock, shares outstanding	66,884,251	67,931,726
Treasury stock, shares	13,649,285	12,601,810