FAIR VALUE MEASUREMENTS - RECURRING BASIS (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Assets
Total	$ 144,361	$ 167,919
Liabilities
Derivatives		16
Money market funds
Assets
Total	4,577	40,342
Government-sponsored enterprise securities
Assets
Total	11,949	6,949
Commercial paper
Assets
Total	35,307	10,999
Corporate notes
Assets
Total	92,528	109,629
Level 1
Assets
Total	4,577	40,342
Level 1 | Money market funds
Assets
Total	4,577	40,342
Level 2
Assets
Total	139,784	127,577
Level 2 | Government-sponsored enterprise securities
Assets
Total	11,949	6,949
Level 2 | Commercial paper
Assets
Total	35,307	10,999
Level 2 | Corporate notes
Assets
Total	$ 92,528	109,629
Level 3
Liabilities
Derivatives		$ 16