Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Allowance for doubtful trade accounts receivable	$ 8,686	$ 7,921
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	67,931,726	69,244,525
Treasury stock, shares	12,601,810	11,289,011