FAIR VALUE MEASUREMENTS - Financial Assets and Liabilities at Fair Value (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Assets, Fair Value Disclosure [Abstract]
Cash and cash equivalents	$ 330,627	$ 199,449
Time deposits and restricted cash	236	30,419
Employee loans	5,981	6,338
Total assets measured at fair value	336,844	236,206
Liabilities, Fair Value Disclosure [Abstract]
Contingent Consideration Classified As Liability, Fair Value Disclosure	800
Total liabilities measured at fair value on a recurring basis	4,835	5,364
Restricted Stock
Liabilities, Fair Value Disclosure [Abstract]
Performance-based equity awards	2,359	5,364
Cash-Settled Award | Restricted Stock Units
Liabilities, Fair Value Disclosure [Abstract]
Cash-settled restricted stock units	1,676
Level 1
Assets, Fair Value Disclosure [Abstract]
Cash and cash equivalents	330,627	199,449
Time deposits and restricted cash	0	0
Employee loans	0	0
Total assets measured at fair value	330,627	199,449
Liabilities, Fair Value Disclosure [Abstract]
Contingent Consideration Classified As Liability, Fair Value Disclosure	0
Total liabilities measured at fair value on a recurring basis	1,676	0
Level 1 | Restricted Stock
Liabilities, Fair Value Disclosure [Abstract]
Performance-based equity awards	0	0
Level 1 | Cash-Settled Award | Restricted Stock Units
Liabilities, Fair Value Disclosure [Abstract]
Cash-settled restricted stock units	1,676
Level 2
Assets, Fair Value Disclosure [Abstract]
Cash and cash equivalents	0	0
Time deposits and restricted cash	236	30,419
Employee loans	0	0
Total assets measured at fair value	236	30,419
Liabilities, Fair Value Disclosure [Abstract]
Contingent Consideration Classified As Liability, Fair Value Disclosure	0
Total liabilities measured at fair value on a recurring basis	0	0
Level 2 | Restricted Stock
Liabilities, Fair Value Disclosure [Abstract]
Performance-based equity awards	0	0
Level 2 | Cash-Settled Award | Restricted Stock Units
Liabilities, Fair Value Disclosure [Abstract]
Cash-settled restricted stock units	0
Level 3
Assets, Fair Value Disclosure [Abstract]
Cash and cash equivalents	0	0
Time deposits and restricted cash	0	0
Employee loans	5,981	6,338
Total assets measured at fair value	5,981	6,338
Liabilities, Fair Value Disclosure [Abstract]
Contingent Consideration Classified As Liability, Fair Value Disclosure	800
Total liabilities measured at fair value on a recurring basis	3,159	5,364
Level 3 | Restricted Stock
Liabilities, Fair Value Disclosure [Abstract]
Performance-based equity awards	2,359	$ 5,364
Level 3 | Cash-Settled Award | Restricted Stock Units
Liabilities, Fair Value Disclosure [Abstract]
Cash-settled restricted stock units	$ 0