Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Current assets
Receivables, allowance for doubtful accounts	$ 15,905	$ 12,221
SHAREHOLDERS' DEFICIT
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized	160,000,000	160,000,000
Common stock, shares issued	95,065,638	95,065,638
Common stock, shares outstanding	55,679,207	56,679,968
Treasury stock, shares	39,386,431	38,385,670