FAIR VALUE MEASUREMENTS FAIR VALUE MEASUREMENTS - Financial Assets and Liabilities Not Measured on Recurring Basis (Details) - Nonrecurring - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Balance
Financial Assets:
Cash and cash equivalents	$ 443,501	$ 362,025
Restricted cash and time deposits	3,318	3,042
Employee loans	5,238	5,978
Balance | Revolving Credit Facility | Credit Facility 2017
Financial Liabilities:
Borrowings	25,018
Balance | Revolving Credit Facility | Credit Facility 2014
Financial Liabilities:
Borrowings		25,019
Estimated Fair Value
Financial Assets:
Cash and cash equivalents	443,501	362,025
Restricted cash and time deposits	3,318	3,042
Employee loans	5,238	5,978
Estimated Fair Value | Revolving Credit Facility | Credit Facility 2017
Financial Liabilities:
Borrowings	25,018
Estimated Fair Value | Revolving Credit Facility | Credit Facility 2014
Financial Liabilities:
Borrowings		25,019
Estimated Fair Value | Level 1
Financial Assets:
Cash and cash equivalents	443,501	362,025
Restricted cash and time deposits	0	0
Employee loans	0	0
Estimated Fair Value | Level 1 | Revolving Credit Facility | Credit Facility 2017
Financial Liabilities:
Borrowings	0
Estimated Fair Value | Level 1 | Revolving Credit Facility | Credit Facility 2014
Financial Liabilities:
Borrowings		0
Estimated Fair Value | Level 2
Financial Assets:
Cash and cash equivalents	0	0
Restricted cash and time deposits	3,318	3,042
Employee loans	0	0
Estimated Fair Value | Level 2 | Credit Facility 2017
Financial Liabilities:
Borrowings	25,018
Estimated Fair Value | Level 2 | Credit Facility 2014
Financial Liabilities:
Borrowings		25,019
Estimated Fair Value | Level 3
Financial Assets:
Cash and cash equivalents	0	0
Restricted cash and time deposits	0	0
Employee loans	5,238	5,978
Estimated Fair Value | Level 3 | Revolving Credit Facility | Credit Facility 2017
Financial Liabilities:
Borrowings	$ 0
Estimated Fair Value | Level 3 | Revolving Credit Facility | Credit Facility 2014
Financial Liabilities:
Borrowings		$ 0