FAIR VALUE (Tables)

3 Months Ended

Mar. 31, 2018

Marketable securities

FAIR VALUE

Schedule of carrying amounts and fair values of assets and liabilities

The cost and fair values of our marketable securities are as follows (dollars in thousands):

	As of March 31, 2018				As of December 31, 2017
			Estimated				Estimated
	Cost		Fair Value		Cost		Fair Value
Marketable securities	$	806	$	923	$	1,007	$	1,166

Long-term debt

FAIR VALUE

Schedule of carrying amounts and fair values of assets and liabilities

The principal amounts and fair values of our debt are as follows (dollars in thousands):

	As of March 31, 2018				As of December 31, 2017
	Principal		Estimated		Principal		Estimated
	Amount		Fair Value		Amount		Fair Value
Total debt	$	3,193,682	$	3,464,617	$	3,211,421	$	3,600,650