Consolidated Condensed Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Allowance for doubtful trade accounts receivable	$ 9,616	$ 10,017
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	71,882,822	72,038,368
Treasury stock, shares	8,650,714	8,495,168