Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Accounts receivable, trade, allowance for doubtful accounts	$ 8,645	$ 10,788
Property and equipment, accumulated depreciation	$ 333,475	$ 293,918
Preferred stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock, shares authorized	45,000,000	45,000,000
Preferred stock, shares issued	0	0
Class A Common Stock
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized	360,000,000	360,000,000
Common stock, shares issued	63,851,000	63,255,000
Common stock, shares outstanding	44,043,000	44,749,000
Treasury stock, shares	19,808,000	18,507,000
Class B Common Stock
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized	90,000,000	90,000,000
Common stock, shares issued	11,484,000	11,484,000