Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Accounts receivable, trade, allowance for doubtful accounts	$ 10,548	$ 11,234
Property and equipment, accumulated depreciation	$ 272,532	$ 261,082
Preferred stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock, shares authorized (in shares)	45,000,000	45,000,000
Preferred stock, shares issued (in shares)	0	0
Class A Common Stock
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	360,000,000	360,000,000
Common stock, shares issued (in shares)	65,324,000	64,568,000
Common stock, shares outstanding (in shares)	30,731,000	29,975,000
Treasury stock, shares (in shares)	34,593,000	34,593,000
Class B Common Stock
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	90,000,000	90,000,000
Common stock, shares issued (in shares)	11,484,000	11,484,000
Common stock, shares outstanding (in shares)	11,484,000	11,484,000