FAIR VALUE MEASUREMENTS - Carrying Value and Fair Value of Debt (Details) - Level 2 - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Carrying Amount
Fair Value And Carrying Value By Balance Sheet Grouping
Total debt	$ 3,851,317	$ 3,844,312
Carrying Amount | Fixed-rate debt
Fair Value And Carrying Value By Balance Sheet Grouping
Total debt	3,372,717	3,371,824
Carrying Amount | Variable-rate debt
Fair Value And Carrying Value By Balance Sheet Grouping
Total debt	478,600	472,488
Fair Value
Fair Value And Carrying Value By Balance Sheet Grouping
Total debt	3,702,440	3,530,433
Fair Value | Fixed-rate debt
Fair Value And Carrying Value By Balance Sheet Grouping
Total debt	3,223,840	3,057,945
Fair Value | Variable-rate debt
Fair Value And Carrying Value By Balance Sheet Grouping
Total debt	$ 478,600	$ 472,488