STOCK-BASED COMPENSATION (Details 3) (USD $)	12 Months Ended			1 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	May 31, 2004	May 31, 2014
Shares
Options exercised (in shares)	(1,515,023)	(621,090)
The 2004 Plan
Stock-based compensation
Total intrinsic value of options exercised	12,100,000	1,600,000	$ 1,700,000
ESPP
Stock-based compensation
Weighted-average grant date fair value of stock purchase rights granted (in dollars per share)	4.05	1.87	$ 1.44
Number of shares authorized under plan	2,500,000
Shares available for future issuance	536,556
ESPP | Minimum
Stock-based compensation
Exercise price of awards as percentage of the fair value of common stock				85.00%
Stock options
Stock-based compensation
Weighted-average grant date fair value of awards granted (in dollars per share)	4.83	3.35	$ 3.09
Total intrinsic value of options exercised	12,100,000	1,700,000	1,800,000
Total fair value of options vested	6,200,000	5,100,000	4,100,000
Total unrecognized compensation expense, net of estimated forfeitures	9,600,000
Average vesting period for recognition of unrecognized compensation expense	1 year 10 months 24 days
Cash received from stock option exercises	8,400,000	2,800,000	1,800,000
Stock options | The 2004 Plan
Stock-based compensation
Number of shares authorized under plan				14,450,000
Vesting period				4 years
Shares
Options outstanding at the beginning of the period (in shares)	6,518,971
Options granted (in shares)	1,605,385
Options exercised (in shares)	(1,515,023)
Options expired (in shares)	(606,999)
Options outstanding at the end of the period (in shares)	6,002,334
Options vested and expected to vest (in shares)	5,581,055
Options exercisable (in shares)	3,491,018
Weighted-Average Exercise Price
Options outstanding at the beginning of the period (in dollars per share)	6.14
Options granted (in dollars per share)	12.64
Options exercised (in dollars per share)	5.52
Options expired (in dollars per share)	8.30
Options outstanding at the end of the period (in dollars per share)	7.84
Options exercisable and expected to become exercisable (in dollars per share)	7.63
Options exercisable (in dollars per share)	6.67
Weighted-Average Remaining Contractual Term
Options outstanding at the end of the period	7 years 1 month 13 days
Options exercisable and expected to become exercisable	7 years 7 days
Options exercisable at the end of the period	6 years 5 months 5 days
Aggregate Intrinsic Value
Options outstanding at the end of the period	49,613,000
Options exercisable and expected to become exercisable	47,317,000
Options exercisable at the end of the period	32,648,000
Stock options | The 2004 Plan | Minimum
Stock-based compensation
Awards vesting by the end of the first year (as a percent)				25.00%
Stock options | The 2004 Plan | Maximum
Stock-based compensation
Term of awards				10 years
Stock options | The 2014 Plan
Stock-based compensation
Number of shares authorized under plan					6,150,000
Shares available for future issuance	5,368,400
Vesting period					4 years
Shares
Options granted (in shares)	753,672
Options expired (in shares)	(8,000)
Options outstanding at the end of the period (in shares)	745,672
Options vested and expected to vest (in shares)	526,914
Options exercisable (in shares)	10,167
Weighted-Average Exercise Price
Options granted (in dollars per share)	13.40
Options expired (in dollars per share)	11.90
Options outstanding at the end of the period (in dollars per share)	13.42
Options exercisable and expected to become exercisable (in dollars per share)	13.40
Options exercisable (in dollars per share)	11.80
Weighted-Average Remaining Contractual Term
Options outstanding at the end of the period	9 years 7 months 10 days
Options exercisable and expected to become exercisable	9 years 7 months 10 days
Options exercisable at the end of the period	9 years 5 months 5 days
Aggregate Intrinsic Value
Options outstanding at the end of the period	2,008,000
Options exercisable and expected to become exercisable	1,429,000
Options exercisable at the end of the period	44,000
Stock options | The 2014 Plan | Minimum
Stock-based compensation
Awards vesting by the end of the first year (as a percent)					25.00%
Stock options | The 2014 Plan | Maximum
Stock-based compensation
Term of awards					10 years
Incentive stock options | The 2004 Plan | Minimum
Stock-based compensation
Exercise price of awards as percentage of the fair value of common stock					100.00%
Nonstatutory stock options | The 2004 Plan | Minimum
Stock-based compensation
Exercise price of awards as percentage of the fair value of common stock					85.00%