Marketable Securities (Tables)

12 Months Ended

Dec. 31, 2020

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, 2020
(Dollars in thousands)	Fair Value		Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Weighted Rate of Return
Money market funds	$	32,815	$	32,815	$	—	$	—	0.01	%
U.S. Government bonds and notes	169,880		169,920		3		(43)		0.12	%
Corporate notes, bonds and commercial paper	238,491		238,509		61		(79)		0.21	%
Total cash equivalents and marketable securities	441,186		441,244		64		(122)
Cash	61,463		61,463		—		—
Total cash, cash equivalents and marketable securities	$	502,649	$	502,707	$	64	$	(122)

	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 and commercial paper	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)

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,
(In thousands)	2020		2019
Cash equivalents	$	74,683	$	58,054
Short-term marketable securities	366,503		305,488
Total cash equivalents and marketable securities	441,186		363,542
Cash	61,463		44,122
Total cash, cash equivalents and marketable securities	$	502,649	$	407,664

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 and gross unrealized losses 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, 2020 and 2019 are as follows:

	Fair Value				Gross Unrealized Loss
(In thousands)	December 31, 2020		December 31, 2019		December 31, 2020		December 31, 2019
Less than 12 months
U.S. Government bonds and notes	$	72,896	$	14,112	$	(43)	$	(1)
Corporate notes, bonds and commercial paper	181,354		250,822		(79)		(63)
Total cash equivalents and marketable securities in a continuous unrealized loss position	$	254,250	$	264,934	$	(122)	$	(64)

Contractual maturities of cash equivalents (excluding money market funds which have no maturity) and marketable securities

The contractual maturities of cash equivalents (excluding money market funds which have no maturity) and marketable securities are summarized as follows:

(In thousands)	December 31, 2020
Due less than one year	$	334,332
Due from one year through three years	74,039
Total	$	408,371