Annual report pursuant to Section 13 and 15(d)

FAIR VALUE MEASUREMENTS - Interest Swap Derivatives (Details)

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FAIR VALUE MEASUREMENTS - Interest Swap Derivatives (Details) - Interest Rate Swap [Member] - Level 2 [Member] - Designated as Hedging Instrument [Member] - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis [Roll Forward]    
Fair value at beginning of period $ 8,159 $ (972)
Designation of interest rate swap as a cash flow hedge   19
Cash flow hedge ineffectiveness 12  
Losses on interest rate swaps reclassified into interest expense from accumulated other comprehensive loss 2,308 2,678
Unrealized losses included in accumulated other comprehensive loss 1,935 6,434
Fair value of end of period $ 12,414 $ 8,159