SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Changes in Cash Flows Due to Adoption of ASU 2016-15 (Details) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net cash provided by operating activities	$ 358,543	$ 135,789	$ 175,928
Net increase in balance	(527,252)	552,046	17,393
Cash, cash equivalents and restricted cash, beginning of period	587,449	34,665	17,247
Cash, cash equivalents and restricted cash, end of period	59,658	587,449	34,665
Previously Reported [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net cash provided by operating activities		133,486	176,739
Net increase in balance		492,231	18,204
Cash, cash equivalents and restricted cash, beginning of period	$ 518,632	25,663	7,434
Cash, cash equivalents and restricted cash, end of period		$ 518,632	$ 25,663