FAIR VALUE MEASUREMENTS (Tables)

12 Months Ended

Dec. 31, 2018

Schedule of fair value hierarchy for financial assets measured at fair value on a recurring basis

Assets and liabilities measured at fair value on a recurring basis are summarized as follows (in thousands):



	Level 1		Level 2		Level 3		Total
December 31, 2018:
Available-for-sale securities	$	—	$	2,309	$	—	$	2,309
Asset retirement obligations ⁽¹⁾	—		—		2,090		2,090


December 31, 2017:
Available-for-sale securities	—		2,271		—		—
Asset retirement obligations ⁽¹⁾	$	—	$	—	$	1,936	$	1,936

⁽¹⁾

We calculate the fair value of asset retirement obligations ("ARO") by discounting the estimated amount using the current Treasury bill rate adjusted for our credit non-performance. At December 31, 2018, the balance is included in "Other long-term liabilities," in the accompanying consolidated balance sheets. At December 31, 2017, $0.2 million and $1.7 million were included in "Other current liabilities" and "Other long-term liabilities," respectively, in the accompanying consolidated balance sheets.

Schedule of changes in asset retirement obligations

The following table provides a summary of changes in our Level 3 asset retirement obligations (in thousands):



	2018		2017			2016
Balance, January 1	$	1,936	$	2,810		$	2,803
Accretion	154		197			207
Subsequent revision of estimated obligation	—		449			—
Payments	—		(1,520		)	(200		)
Balance, December 31	$	2,090	$	1,936		$	2,810

Fair Value, by Balance Sheet Grouping

The fair values of our Level 2 available-for-sale debt securities, based upon quoted prices for similar items in active markets, are as follows (in thousands):



	December 31, 2018
	Cost		Unrealized Gain		Unrealized Loss			Fair Value
Japanese Corporate Bonds	$	2,184	$	144	$	(107	)	$	2,221
Japanese Government Bonds	87		5		(4		)	88
Total Bonds	$	2,271	$	149	$	(111	)	$	2,309

	December 31, 2017
	Cost		Unrealized Gain		Unrealized Loss			Fair Value
Japanese Corporate Bonds	$	2,267	$	17	$	(100	)	$	2,184
Japanese Government Bonds	87		1		(1		)	87
Total Bonds	$	2,354	$	18	$	(101	)	$	2,271

Schedule of fair value of term loan and revolving credit facility

The fair values of our other Level 2 debt liabilities, based upon quoted prices for similar items in active markets, are as follows (in thousands):



	December 31,
	2018				2017
	Carrying Amount		Fair Value		Carrying Amount		Fair Value
Term loan	$	429,143	$	428,071	$	298,500	$	301,485
Revolving credit facility	—		—		5,000		5,050