Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Stockholders' equity (deficit)
Allowance for doubtful accounts	$ 2,700	$ 2,920
Preferred stock par value	$ 0.01	$ 0.01
Preferred stock authorized	20,000,000	20,000,000
Preferred stock, issued	0	0
Preferred stock, outstanding	0	0
Class A common stock
Stockholders' equity (deficit)
Preferred stock authorized	250,000,000	250,000,000
Common stock, par value	$ 0.01	$ 0.01
Common stock, issued	36,758,233	18,935,916
Common stock, outstanding	36,749,072	18,935,916
Class B common stock
Stockholders' equity (deficit)
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, authorized	75,000,000	75,000,000
Common stock, issued	69,066,445	69,066,445
Common stock, outstanding	50,836,629	62,002,729
Class C common stock
Stockholders' equity (deficit)
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, authorized	1	1
Common stock, issued	1	1
Common stock, outstanding	1	1