CONCENTRATION OF CREDIT RISK AND MAJOR CUSTOMERS (Details) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2017 USD ($) customer	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Major Customers
Total revenues	$ 483,130	$ 453,087	$ 398,619	$ 461,005	$ 527,291	$ 551,966	$ 439,041	$ 412,725	$ 1,795,841	$ 1,931,023	$ 2,273,311
Trade receivables	$ 181,671				152,032				$ 181,671	152,032
Revenues | Customer Concentration Risk | Major customers
Major Customers
Number of customers | customer									0
Revenues | Customer Concentration Risk | Customer A
Major Customers
Total revenues										253,465	343,483
Revenues | Customer Concentration Risk | Customer B
Major Customers
Total revenues										241,255	305,048
Revenues | Customer Concentration Risk | Customer C
Major Customers
Total revenues										265,642	312,150
Trade accounts receivable | Customer Concentration Risk | Major customers
Major Customers
Trade receivables					$ 42,500					$ 42,500	$ 48,400