FAIR VALUE MEASUREMENTS - Carrying Value and Fair Value of Debt (Details) - Level 2 - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Carrying Amount
Fair Value And Carrying Value By Balance Sheet Grouping
Total debt	$ 4,779,045	$ 4,217,695
Carrying Amount | Fixed-rate debt
Fair Value And Carrying Value By Balance Sheet Grouping
Total debt	3,846,426	3,967,695
Carrying Amount | Variable-rate debt
Fair Value And Carrying Value By Balance Sheet Grouping
Total debt	932,619	250,000
Fair Value
Fair Value And Carrying Value By Balance Sheet Grouping
Total debt	4,949,835	4,333,488
Fair Value | Fixed-rate debt
Fair Value And Carrying Value By Balance Sheet Grouping
Total debt	4,016,825	4,083,488
Fair Value | Variable-rate debt
Fair Value And Carrying Value By Balance Sheet Grouping
Total debt	$ 933,010	$ 250,000