Fair Value of Financial Instruments (Tables)

12 Months Ended

Dec. 31, 2017

Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]

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 December 31, 2017 and 2016:

	As of December 31, 2017
	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	$	10,915	$	10,915	$	—	$	—
U.S. Government bonds and notes	55,220		—		55,220		—
Corporate notes, bonds, commercial paper and other	195,073		1,058		194,015		—
Total available-for-sale securities	$	261,208	$	11,973	$	249,235	$	—

	As of December 31, 2016
	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	$	10,681	$	10,681	$	—	$	—
U.S. Government bonds and notes	48,292		—		48,292		—
Corporate notes, bonds, commercial paper and other	62,178		303		61,875		—
Total available-for-sale securities	$	121,151	$	10,984	$	110,167	$	—

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 which require fair value disclosure as of December 31, 2017 and 2016:

	As of December 31, 2017						As of December 31, 2016
(in thousands)	Face Value		Carrying Value		Fair Value		Face Value		Carrying Value		Fair Value
1.375% Convertible Senior Notes due 2023	$	172,500	$	135,447	$	173,450	$	—	$	—	$	—
1.125% Convertible Senior Notes due 2018	$	81,207	$	78,451	$	100,802	$	138,000	$	126,167	$	173,961