Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
CURRENT ASSETS:
Allowance for accounts receivable	$ 310	$ 472
Preferred stock
Par value (in dollars per share)	$ 0.001	$ 0.001
Shares authorized (in shares)	10,000,000	10,000,000
Shares issued (in shares)	0	0
Shares outstanding (in shares)	0	0
Class A Common Stock
Common stock
Par value (in dollars per share)	$ 0.001	$ 0.001
Shares authorized (in shares)	750,000,000	750,000,000
Shares issued (in shares)	49,553,000	35,938,000
Shares outstanding (in shares)	49,553,000	35,938,000
Class B Common Stock
Common stock
Par value (in dollars per share)	$ 0.001	$ 0.001
Shares authorized (in shares)	300,000,000	300,000,000
Shares issued (in shares)	160,200,000	173,624,000
Shares outstanding (in shares)	160,200,000	173,624,000
Class C Common Stock
Common stock
Par value (in dollars per share)	$ 0.001	$ 0.001
Shares authorized (in shares)	75,000,000	75,000,000
Shares issued (in shares)	42,945,000	42,945,000
Shares outstanding (in shares)	42,945,000	42,945,000