FAIR VALUE MEASUREMENTS - Carrying Value and Fair Value of Debt (Details) - Level 2 - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Carrying Amount
Fair Value And Carrying Value By Balance Sheet Grouping
Total debt	$ 3,844,312	$ 3,534,618
Carrying Amount | Fixed-rate debt
Fair Value And Carrying Value By Balance Sheet Grouping
Total debt	3,371,824	3,368,618
Carrying Amount | Variable-rate debt
Fair Value And Carrying Value By Balance Sheet Grouping
Total debt	472,488	166,000
Fair Value
Fair Value And Carrying Value By Balance Sheet Grouping
Total debt	3,530,433	3,631,973
Fair Value | Fixed-rate debt
Fair Value And Carrying Value By Balance Sheet Grouping
Total debt	3,057,945	3,465,973
Fair Value | Variable-rate debt
Fair Value And Carrying Value By Balance Sheet Grouping
Total debt	$ 472,488	$ 166,000