Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Allowance for doubtful trade accounts receivable	$ 9,169	$ 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	65,790,112	67,931,726
Treasury stock, shares	14,743,424	12,601,810