DERIVATIVE FINANCIAL INSTRUMENTS AND HEDGING - Gain or Loss Recognized on Derivative Financial Instruments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Derivative instruments, gain (loss) recognized
Total interest expense and other finance expense presented in the Consolidated Statement of Operations in which the effects of cash flow hedges are recorded	$ (29,687)	$ (28,091)	$ (30,414)
Cash flow hedges | Interest rate swaps
Derivative instruments, gain (loss) recognized
Gain (loss) recognized in accumulated other comprehensive income on derivative financial instruments	1,703	(497)	(1,846)
Loss recognized in other expense	0	0	(1)
Total interest expense and other finance expense presented in the Consolidated Statement of Operations in which the effects of cash flow hedges are recorded	(29,687)	(28,091)	(30,414)
Cash flow hedges | Interest rate swaps | Interest expense
Derivative instruments, gain (loss) recognized
Loss reclassified from accumulated other comprehensive income to interest expense	$ (734)	$ (1,190)	$ (1,927)