FAIR VALUE MEASUREMENTS (Fair Value by Balance Sheet Grouping) (Details) - Estimate of Fair Value Measurement - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Series 2012 Bonds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notes payable, fair value disclosure	$ 41,545	$ 42,633
Series 2016 Bonds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notes payable, fair value disclosure	147,261	149,582
Senior Notes due 2022
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notes payable, fair value disclosure	732,774	551,144
Senior Notes due 2025
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notes payable, fair value disclosure	$ 463,455	$ 283,965