INCOME TAXES - Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Deferred tax assets:
Net operating loss carryforwards	$ 40,357	$ 36,626
Research and development credits	5,192	4,720
Accruals and reserves	3,044	1,304
Deferred revenue	10,068	3,558
Stock-based compensation	2,290	1,510
Other	440	276
Gross deferred tax assets	61,391	47,994
Valuation allowance	(58,838)	(47,992)
Total deferred tax assets	2,553	2
Deferred tax liabilities:
internally developed software	(2,303)	0
Goodwill	(63)	(52)
Gross deferred tax liabilities	(2,366)	(52)
Net deferred tax assets	$ 187
Net deferred tax liabilities		$ (50)