SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Leases (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Jan. 01, 2019
Operating Leased Assets [Line Items]
Adoption of ASC 842,leases			$ 128,908
Right-of-use asset, amortization of gain (loss)	$ 5,300	$ 5,300
Retained Earnings
Operating Leased Assets [Line Items]
Adoption of ASC 842,leases			$ 128,908