Net Income Per Share - Computation of Basic and Diluted Net Income Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Basic:
Net income	$ 564	$ 1,283	$ 1,238	$ 3,697
Net income allocable to preferred stockholders		778		2,559
Net income allocable to common stockholders	564	505	1,238	1,138
Diluted:
Net income	564	1,283	1,238	3,697
Net income allocable to preferred stockholders		737		2,425
Net income allocable to common stockholders	$ 564	$ 546	$ 1,238	$ 1,272
Denominator:
Weighted-average shares outstanding in computing basic net income per share allocable to common stockholders	17,045,689	5,827,662	16,936,898	4,515,414
Effect of potentially dilutive securities:
Stock awards	876,946	839,709	1,102,506	812,271
Weighted-average shares used in computing diluted net income per common share allocable to common stockholders	17,922,635	6,667,371	18,039,404	5,327,685
Net income per common share:
Basic	$ 0.03	$ 0.09	$ 0.07	$ 0.25
Diluted	$ 0.03	$ 0.08	$ 0.07	$ 0.24