Marketable Securities (Tables)

12 Months Ended

Dec. 31, 2018

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, 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	)



	As of December 31, 2017
(Dollars in thousands)	Fair Value		Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Weighted Rate of Return
Money market funds	$	10,915	$	10,915	$	—	$	—		1.16	%
U.S. Government bonds and notes	55,220		55,221		—		(1		)	1.12	%
Corporate notes, bonds, commercial paper and other	195,073		195,204		—		(131		)	1.39	%
Total cash equivalents and marketable securities	261,208		261,340		—		(132		)
Cash	68,168		68,168		—		—
Total cash, cash equivalents and marketable securities	$	329,376	$	329,508	$	—	$	(132	)

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, 2018		December 31, 2017
	(Dollars in thousands)
Cash equivalents	$	64,868	$	157,676
Short term marketable securities	161,840		103,532
Total cash equivalents and marketable securities	226,708		261,208
Cash	51,056		68,168
Total cash, cash equivalents and marketable securities	$	277,764	$	329,376

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, 2018 and 2017 are as follows:



	Fair Value				Gross Unrealized Loss
	December 31, 2018		December 31, 2017		December 31, 2018			December 31, 2017
	(In thousands)
Less than one year
U.S. Government bonds and notes	$	32,630	$	42,581	$	(4	)	$	(1	)
Corporate notes, bonds and commercial paper	183,998		194,015		(97		)	(131		)
Total Corporate notes, bonds, and commercial paper and U.S. Government bonds and notes	$	216,628	$	236,596	$	(101	)	$	(132	)