FAIR VALUE MEASUREMENTS - Assets and Liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Asset:
Marketable securities, available-for-sale	$ 200,359	$ 191,799
Recurring basis
Asset:
Marketable securities, available-for-sale	200,359	191,799
Liabilities:
Derivative liability related to warrants	33,360	38,810
Business combination-related contingent consideration	86,377	59,021
Recurring basis | Significant other observable inputs (Level 2)
Asset:
Marketable securities, available-for-sale	200,359	191,799
Recurring basis | Significant unobservable inputs (Level 3)
Liabilities:
Derivative liability related to warrants	33,360	38,810
Business combination-related contingent consideration	$ 86,377	$ 59,021