Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares shares in Thousands	Sep. 30, 2019	Dec. 31, 2018
Common stock, shares outstanding	23,302	21,620
Class A common stock
Common stock, par value	$ 0.001	$ 0.001
Common stock authorized	125,000	125,000
Common Stock, Shares, Issued	23,302	21,620
Common stock, shares outstanding	23,302	21,620
Class B common stock
Common stock, par value	$ 0.001	$ 0.001
Common stock authorized	100,000	100,000
Common Stock, Shares, Issued	4,957	6,547
Common stock, shares outstanding	4,957	6,547