Financial Instruments (Tables)

12 Months Ended

Dec. 31, 2023

Fair Value Disclosures [Abstract]

Summary of Investments

Investments consist of the following as of December 31, 2023 and 2022 (dollars in thousands):

	December 31, 2023
			Gross Unrealized
	Cost		Gain		(Loss)			Fair Value
Short-term investments (available for sale):
Non-governmental debt securities	$	245,886	$	719	$	(892	)	$	245,713
Treasury and federal agencies		239,859		393		(830	)		239,422
Total short-term investments (available for sale)	$	485,745	$	1,112	$	(1,722	)	$	485,135

	December 31, 2022
			Gross Unrealized
	Cost		Gain		(Loss)			Fair Value
Short-term investments (available for sale):
Municipal bonds	$	3,016	$	-	$	(22	)	$	2,994
Non-governmental debt securities		222,575		37		(2,880	)		219,732
Treasury and federal agencies		179,068		6		(2,485	)		176,589
Total short-term investments (available for sale)	$	404,659	$	43	$	(5,387	)	$	399,315

Schedule of Available-for-Sale Investments

A schedule of available-for-sale investments segregated by their original stated terms to maturity as of December 31, 2023 and 2022 are as follows (dollars in thousands):

	Less than one year		One to five years		Total
Original stated term to maturity of available-for-sale-    investments as of December 31, 2023	$	251,070	$	234,065	$	485,135
Original stated term to maturity of available-for-sale-    investments as of December 31, 2022	$	188,472	$	210,843	$	399,315

Schedule of Maintenance Fee Payment to our equity affiliate

We make periodic operating maintenance payments to our equity affiliate. The total fees recorded for the years ended December 31, 2023, 2022 and 2021 were as follows (dollars in thousands):

For the year ended December 31, 2023	$	1,672
For the year ended December 31, 2022	$	1,578
For the year ended December 31, 2021	$	1,726