CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Accounts receivable, net of allowance for doubtful accounts of $2,379 and $2,590, respectively	$ 2,379	$ 2,590
Class A Common Stock
Common Stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common Stock, shares authorized (in shares)	500,000,000	500,000,000
Common Stock, shares issued (in shares)	68,897,723	76,071,145
Common Stock, shares outstanding (in shares)	68,897,723	76,071,145
Class B Common Stock
Common Stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common Stock, shares authorized (in shares)	140,000,000	140,000,000
Common Stock, shares issued (in shares)	25,670,684	25,670,684
Common Stock, shares outstanding (in shares)	25,670,684	25,670,684