Net Income (Loss) Per Share Attributable to Common Stockholders - Calculation of Basic and Diluted Net Loss Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Numerator:
Income (loss) from continuing operations, net of income taxes	$ (389)	$ (2,801)	$ (1,484)	$ (4,333)	$ 1,438	$ (1,581)	$ (2,960)	$ (6,127)	$ (9,007)	$ (9,230)	$ (19,700)
Total income (loss) from discontinued operations, net of income taxes					(1)	0	(161)	26	0	(136)	21,927
Net income (loss)	$ (389)	$ (2,801)	$ (1,484)	$ (4,333)	$ 1,437	$ (1,581)	$ (3,121)	$ (6,101)	$ (9,007)	$ (9,366)	$ 2,227
Denominator:
Weighted-average number of shares of common stock outstanding for basic and diluted net loss per share attributable to common stockholders	46,710,402	46,158,465	45,702,810	44,831,453					45,864,500	51,764,506	50,511,366
Basic and diluted net income (loss) per share:
Loss from continuing operations (usd per share)	$ (0.01)	$ (0.06)	$ (0.03)	$ (0.10)					$ (0.20)	$ (0.18)	$ (0.39)
Income from discontinued operations (usd per share)									0	0	0.43
Net income (loss) (usd per share)	$ (0.01)	$ (0.06)	$ (0.03)	$ (0.10)					$ (0.20)	$ (0.18)	$ 0.04