FAIR VALUE MEASUREMENTS - ASSETS AND LIABILITIES MEASURED AT FAIR VALUE ON A RECURRING BASIS (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Assets:
Short-term investments	$ 1,032	$ 4,026
Fair Value, Measurements, Recurring | Level 1
Assets:
Short-term investments	1,032	4,026
Embedded derivative in lease agreement	0	0
Liabilities:
Acquisition-related contingent consideration	0	0
Fair Value, Measurements, Recurring | Level 1 | Interest rate swap agreements
Liabilities:
Interest rate swap agreements	0	0
Fair Value, Measurements, Recurring | Level 1 | Colombian Long Term Credit Facility | Interest rate swap agreements
Assets:
Interest rate swap agreements	0	0
Fair Value, Measurements, Recurring | Level 2
Assets:
Short-term investments	0	0
Embedded derivative in lease agreement	0	0
Liabilities:
Acquisition-related contingent consideration	0	0
Fair Value, Measurements, Recurring | Level 2 | Interest rate swap agreements
Liabilities:
Interest rate swap agreements	22,409	24,682
Fair Value, Measurements, Recurring | Level 2 | Colombian Long Term Credit Facility | Interest rate swap agreements
Assets:
Interest rate swap agreements	0	3
Fair Value, Measurements, Recurring | Level 3
Assets:
Short-term investments	0	0
Embedded derivative in lease agreement	12,623	13,290
Liabilities:
Acquisition-related contingent consideration	16,045	15,444
Fair Value, Measurements, Recurring | Level 3 | Interest rate swap agreements
Liabilities:
Interest rate swap agreements	0	0
Fair Value, Measurements, Recurring | Level 3 | Colombian Long Term Credit Facility | Interest rate swap agreements
Assets:
Interest rate swap agreements	$ 0	$ 0