Marketable Securities (Tables)

12 Months Ended

Dec. 31, 2019

Debt Securities, Available-for-sale [Abstract]

Cash equivalents and marketable securities classified as available-for-sale

Total cash, cash equivalents and marketable securities are summarized as follows:



	As of December 31, 2019
(Dollars in thousands)	Fair Value		Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Weighted Rate of Return
Money market funds	$	10,065	$	10,065	$	—	$	—		1.48	%
U.S. Government bonds and notes	39,086		39,087		—		(1		)	1.49	%
Corporate notes, bonds, commercial paper and other	314,391		314,435		19		(63		)	1.81	%
Total cash equivalents and marketable securities	363,542		363,587		19		(64		)
Cash	44,122		44,122		—		—
Total cash, cash equivalents and marketable securities	$	407,664	$	407,709	$	19	$	(64	)



	As of December 31, 2018
(Dollars in thousands)	Fair Value		Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Weighted Rate of Return
Money market funds	$	10,080	$	10,080	$	—	$	—		2.23	%
U.S. Government bonds and notes	32,630		32,634		—		(4		)	2.28	%
Corporate notes, bonds, commercial paper and other	183,998		184,095		—		(97		)	2.37	%
Total cash equivalents and marketable securities	226,708		226,809		—		(101		)
Cash	51,056		51,056		—		—
Total cash, cash equivalents and marketable securities	$	277,764	$	277,865	$	—	$	(101	)

Available-for-sale securities reported at fair value

Available-for-sale securities are reported at fair value on the balance sheets and classified as follows:



	As of
	December 31, 2019		December 31, 2018
	(Dollars in thousands)
Cash equivalents	$	58,054	$	64,868
Short term marketable securities	305,488		161,840
Total cash equivalents and marketable securities	363,542		226,708
Cash	44,122		51,056
Total cash, cash equivalents and marketable securities	$	407,664	$	277,764

Estimated fair value of cash equivalents and marketable securities classified by date of contractual maturity and the length of time that the securities have been in a continuous unrealized loss position

The estimated fair value of cash equivalents and marketable securities classified by the length of time that the securities have been in a continuous unrealized loss position at December 31, 2019 and 2018 are as follows:



	Fair Value				Gross Unrealized Loss
	December 31, 2019		December 31, 2018		December 31, 2019			December 31, 2018

	(In thousands)
Less than one year
U.S. Government bonds and notes	$	14,112	$	32,630	$	(1	)	$	(4	)
Corporate notes, bonds and commercial paper	250,822		183,998		(63		)	(97		)
Total Corporate notes, bonds, and commercial paper and U.S. Government bonds and notes	$	264,934	$	216,628	$	(64	)	$	(101	)