INCOME TAXES - Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred tax assets
Stock-based compensation	$ 997	$ 1,899
Federal benefit of state uncertain tax positions	919	1,392
Accrued vacation	660	1,035
Deferred rent	119	275
State net operating loss carryforwards	266	222
Allowance for doubtful accounts	135	160
Other	316	299
Deferred tax assets, gross, total	3,412	5,282
Less: Valuation allowance	(257)	(189)
Total	3,155	5,093
Deferred tax liabilities
Property and equipment & capitalized internal use software development costs	(2,488)	(2,786)
Net deferred tax asset	$ 667	$ 2,307