Fair Value of Financial Instruments (Tables)

6 Months Ended

Jun. 30, 2019

Fair Value Disclosures [Abstract]

Summary of the valuation of cash equivalents and marketable securities by pricing levels

The following table presents the financial instruments that are carried at fair value and summarizes the valuation of its cash equivalents and marketable securities by the above pricing levels as of June 30, 2019 and December 31, 2018:

	As of June 30, 2019
	Total		Quoted  Market  Prices in  Active  Markets  (Level 1)		Significant  Other  Observable  Inputs  (Level 2)		Significant  Unobservable  Inputs  (Level 3)
	(In thousands)
Money market funds	$	38,437	$	38,437	$	—	$	—
U.S. Government bonds and notes	28,178		—		28,178		—
Corporate notes, bonds, commercial paper and other	234,428		—		234,428		—
Total available-for-sale securities	$	301,043	$	38,437	$	262,606	$	—

	As of December 31, 2018
	Total		Quoted  Market  Prices in  Active  Markets  (Level 1)		Significant  Other  Observable  Inputs  (Level 2)		Significant  Unobservable  Inputs  (Level 3)
	(In thousands)
Money market funds	$	10,080	$	10,080	$	—	$	—
U.S. Government bonds and notes	32,630		—		32,630		—
Corporate notes, bonds, commercial paper and other	183,998		—		183,998		—
Total available-for-sale securities	$	226,708	$	10,080	$	216,628	$	—

Financial instruments not carried at fair value but requiring fair value disclosure

The following table presents the financial instruments that are not carried at fair value but require fair value disclosure as of June 30, 2019 and December 31, 2018:

	As of June 30, 2019						As of December 31, 2018
(In thousands)	Face  Value		Carrying  Value		Fair Value		Face  Value		Carrying  Value		Fair Value
1.375% Convertible Senior Notes due 2023 (the "2023 Notes")	$	172,500	$	145,314	$	169,266	$	172,500	$	141,934	$	150,075