Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Property and equipment, accumulated depreciation	$ 347,302	$ 293,918
Accounts receivable, trade, allowance for doubtful accounts	$ 5,733	$ 10,788
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
Treasury stock (in shares)	19,808,000	18,507,000
Common Class A [Member]
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)	63,886,000	63,255,000
Common stock, shares, outstanding (in shares)	44,078,000	44,749,000
Common Class B [Member]
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