Basic and Diluted Net Income (Loss) Per Common Share - Summary of Allocation for Net Income (Loss) Available to Stockholders (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Numerator
Net income (loss)	$ (1,998)	$ 2,567	$ (5,367)	$ (8,271)
Allocation of net income (loss) to Class A and B common stockholders and Series C convertible preferred stockholders for basic net income (loss) per share:
Basic net income (loss) per share	(1,998)	2,567	(5,367)	(8,271)
Class A common stock
Allocation of net income (loss) to Class A and B common stockholders and Series C convertible preferred stockholders for basic net income (loss) per share:
Basic net income (loss) per share	(1,152)	1,472	(3,090)	(4,742)
Class B common stock
Allocation of net income (loss) to Class A and B common stockholders and Series C convertible preferred stockholders for basic net income (loss) per share:
Basic net income (loss) per share	(639)	827	(1,719)	(2,664)
Series C convertible preferred stock
Allocation of net income (loss) to Class A and B common stockholders and Series C convertible preferred stockholders for basic net income (loss) per share:
Basic net income (loss) per share	$ (207)	$ 268	$ (558)	$ (865)