EQUITY AWARD PLAN (Stock-based Compensation Expense) (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Employee Service Share-based Compensation, Allocation of Recognized Period Costs
Total stock-based compensation	$ 26,594,000	$ 19,115,000	$ 8,451,000
Tax benefit from stock-based compensation	(688,000)	(1,535,000)	(2,417,000)
Total stock-based compensation, net of tax effect	25,906,000	17,580,000	6,034,000
Compensation cost not yet recognized	64,300,000
Compensation cost not yet recognized, period for recognition	2 years 2 months 13 days
Cost of revenue
Employee Service Share-based Compensation, Allocation of Recognized Period Costs
Total stock-based compensation	1,092,000	818,000	243,000
Research and development
Employee Service Share-based Compensation, Allocation of Recognized Period Costs
Total stock-based compensation	9,099,000	6,738,000	2,409,000
Sales and marketing
Employee Service Share-based Compensation, Allocation of Recognized Period Costs
Total stock-based compensation	7,180,000	4,922,000	1,787,000
General and administrative
Employee Service Share-based Compensation, Allocation of Recognized Period Costs
Total stock-based compensation	9,223,000	6,637,000	4,012,000
YFind Employee Stock Compensation Plan [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs
Stock-based compensation related to the cash settlement of equity awards		$ 400,000