CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Allowance for doubtful accounts receivable	$ 576	$ 740
Preferred stock, par value	$ 0.01
Preferred stock, shares authorized	10,000,000
Preferred stock, shares issued	0
Preferred stock, shares outstanding	0
Common stock, shares outstanding	74,889,772
Class A Common Stock
Common stock, par value	$ 0.01
Common stock, shares authorized	300,000,000
Common stock, shares issued	37,654,000
Common stock, shares outstanding	37,653,630
Class B Common Stock
Common stock, par value	$ 0.01
Common stock, shares authorized	215,000,000
Common stock, shares issued	37,236,000
Common stock, shares outstanding	37,236,142