FAIR VALUE OF FINANCIAL INSTRUMENTS (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Carrying Value
Estimated fair values of financial instruments
Cash and cash equivalents	$ 160,802	$ 200,501
Restricted Cash	1,472	1,468
Long-term debt, including current portion, excluding discount	1,336,941	1,361,826
Fair Value
Estimated fair values of financial instruments
Cash and cash equivalents	160,802	200,501
Restricted Cash	1,472	1,468
Long-term debt, including current portion, excluding discount	$ 1,327,763	$ 1,351,474