Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2017

Fair Value Disclosures [Abstract]

Valuation of Company's Assets and Liabilities Measured at Fair Value

The following table summarizes the valuation of the Company’s assets and liabilities measured at fair value as categorized based on the hierarchy described in Note 2.

	Level 1		Level 2			Level 3		Total
	(In thousands)
As of December 31, 2017
Money market funds	$	88,562	$	—		$	—	$	88,562
Securities available-for-sale
Corporate debt		—		145,052			—		145,052
Trading securities
Corporate debt		—		91,302			—		91,302
Mutual funds held in rabbi trust		—		3,167			—		3,167
Foreign currency forward position		—		(702	)		—		(702	)
Total	$	88,562	$	238,819		$	—	$	327,381
As of December 31, 2016
Money market funds	$	58,573	$	—		$	—	$	58,573
Securities available-for-sale
Corporate debt		—		118,870			—		118,870
Trading securities
Corporate debt		—		74,207			—		74,207
Mutual funds held in rabbi trust		—		1,327			—		1,327
Foreign currency forward position		—		(266	)		—		(266	)
Total	$	58,573	$	194,138		$	—	$	252,711

Summary of Foreign Currency Forward Contracts

A summary of the foreign currency forward position is as follows:

	As of December 31,
	2017			2016
	(In thousands)
Notional value	$	84,422		$	66,972
Fair value of notional		85,124			67,238
Fair value of the (liability)	$	(702	)	$	(266	)

Summary of Company's Investments

The following is a summary of the Company’s investments:

	Amortized cost		Gross unrealized gains		Gross unrealized losses			Estimated fair value
	(In thousands)
As of December 31, 2017
Securities available-for-sale
Corporate debt	$	145,526	$	9	$	(483	)	$	145,052
Trading securities
Corporate debt		91,578		30		(306	)		91,302
Mutual funds held in rabbi trust		2,729		438		—			3,167
Total trading securities		94,307		468		(306	)		94,469
Total investments	$	239,833	$	477	$	(789	)	$	239,521
As of December 31, 2016
Securities available-for-sale
Corporate debt	$	119,073	$	13	$	(216	)	$	118,870
Trading securities
Corporate debt		74,394		47		(234	)		74,207
Mutual funds held in rabbi trust		1,212		115		—			1,327
Total trading securities		75,606		162		(234	)		75,534
Total investments	$	194,679	$	175	$	(450	)	$	194,404

Summary of Fair Value of Investments Based upon Contractual Maturities

The following table summarizes the fair value of the investments based upon the contractual maturities:

	As of December 31,
	2017		2016
	(In thousands)
Less than one year	$	130,738	$	117,904
Due in 1 - 5 years		108,783		76,500
Total	$	239,521	$	194,404

Fair Values and Unrealized Losses on Investments

The following table provides fair values and unrealized losses on investments and by the aging of the securities' continuous unrealized loss position as of December 31, 2017 and 2016 respectively:  

	Less than Twelve Months					Twelve Months or More					Total
	Estimated fair value		Gross unrealized losses			Estimated fair value		Gross unrealized losses			Estimated fair value		Gross unrealized losses
	(In thousands)
As of December 31, 2017
Corporate debt	$	177,114	$	(536	)	$	26,476	$	(253	)	$	203,590	$	(789	)
As of December 31, 2016
Corporate debt	$	136,667	$	(449	)	$	2,000	$	(1	)	$	138,667	$	(450	)