Net Income (Loss) per Share - Calculation of Basic and Diluted Net Income (Loss) per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Numerator:
Net income (loss)	$ 2,916	$ (1,213)
Less: Income allocated to preferred stockholders	(2,916)	0
Net income (loss) attributable to common stockholders	$ 0	$ (1,213)
Denominator:
Weighted-average common shares outstanding, basic and diluted (in shares)	3,031	2,600
Net income (loss) per share:
Net income (loss) per share attributable to common stockholders, basic and diluted (in dollars per share)	$ 0.00	$ (0.47)