COMMITMENTS AND CONTINGENCIES - Operating Leases (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Future minimum lease payments, Other Operating Leases
2018	$ 10,067
2019	5,826
2020	1,366
Total future minimum lease payments	17,259
Rental expense	16,100	$ 17,000	$ 11,700
Other Operating Leases, Affiliate
Future minimum lease payments, Other Operating Leases
2018	240
Total future minimum lease payments	240
Other Operating Leases, Others
Future minimum lease payments, Other Operating Leases
2018	9,827
2019	5,826
2020	1,366
Total future minimum lease payments	$ 17,019