EMPLOYEE STOCK PLANS - Narrative (Details) - USD ($) $ / shares in Units, $ in Millions		1 Months Ended		12 Months Ended
	May. 28, 2015	May. 31, 2014	Dec. 31, 2013	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percent of options vesting on first anniversary of vesting commencement date				25.00%
Options granted in period (in shares)				716,000	746,000	1,600,000
Options, grant date fair value				$ 1.2	$ 0.9	$ 1.4
Defined contribution plan, employer discretionary contribution amount				$ 0.2	$ 0.2	$ 0.1
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting rate				2.78%
Time-based restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting rate			25.00%
Time-based restricted stock units | Prior to May 28, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grant ratio				1.75
Time-based restricted stock units | On or after May 28, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grant ratio				1.00
2012 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares available for future grant (in shares)				4,100,000
Number of shares of additional common stock approved (in shares)	2,500,000
Number of shares reserved for issuance (in shares)	19,500,000
Grant ratio	1.75
2012 Equity Incentive Plan | Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Exercise price, as a percent of fair market value of common stock on grant date				100.00%
Percent of options vesting on first anniversary of vesting commencement date				25.00%
Vesting period				36 months
Employee requisite service period			1 year
2012 Equity Incentive Plan | Maximum | Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award terms				7 years
1994 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
ESPP extended term		10 years
ESPP offering period				6 months
1994 Plan | Employee stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares available for future grant (in shares)				2,400,000
Number of shares reserved for issuance (in shares)				6,200,000
Exercise price, as a percent of fair market value of common stock on grant date				90.00%
Maximum employee subscription rate				15.00%
Maximum number of shares per employee (in shares)				4,000		2,000
Shares issued in period (in shares)				100,000
Average price of shares purchased, per share (in usd per share)			$ 2.09	$ 2.99	$ 2.17	$ 2.09