NET INCOME PER SHARE - Calculation of net income per share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017
Earnings Per Share [Abstract]
Net income	$ 639	$ 1,277	$ (188)	$ (495)	$ (559)	$ 1,145	$ 114	$ 301	$ 1,233	$ 1,001
Shares outstanding:
Weighted-average common shares outstanding (in shares)									21,544	21,814
Additional dilutive common stock equivalents (in shares)									61	63
Diluted shares outstanding (in shares)									21,605	21,877
Net income per share - basic (in dollars per share)	$ 0.03	$ 0.06	$ (0.01)	$ (0.02)	$ (0.03)	$ 0.05	$ 0.01	$ 0.01	$ 0.06	$ 0.05
Net income per share - diluted (in dollars per share)	$ 0.03	$ 0.06	$ (0.01)	$ (0.02)	$ (0.03)	$ 0.05	$ 0.01	$ 0.01	$ 0.06	$ 0.05