Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2018

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, 2018
Money market funds	$	112,529	$	—		$	—	$	112,529
Securities available-for-sale
Corporate debt		—		146,966			—		146,966
Trading securities
Corporate debt		—		71,861			—		71,861
U.S. Treasuries		—		17,178			—		17,178
Mutual funds held in rabbi trust		—		4,100			—		4,100
Foreign currency forward position		—		(1,021	)		—		(1,021	)
Total	$	112,529	$	239,084		$	—	$	351,613
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

Summary of Foreign Currency Forward Contracts

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

	As of December 31,
	2018			2017
	(In thousands)
Notional value	$	106,306		$	84,422
Fair value of notional		107,327			85,124
Fair value of the (liability)	$	(1,021	)	$	(702	)

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, 2018
Securities available-for-sale
Corporate debt	$	147,556	$	27	$	(617	)	$	146,966
Trading securities
Corporate debt		72,274		8		(421	)		71,861
U.S. Treasuries		16,953		225		—			17,178
Mutual funds held in rabbi trust		4,347		—		(247	)		4,100
Total trading securities		93,574		233		(668	)		93,139
Total investments	$	241,130	$	260	$	(1,285	)	$	240,105
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

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,
	2018		2017
	(In thousands)
Less than one year	$	134,255	$	130,738
Due in 1 - 5 years		105,850		108,783
Total	$	240,105	$	239,521

Fair Values and Unrealized Losses on Corporate Debt Investments

The following table provides fair values and unrealized losses on corporate debt investments and by the aging of the securities' continuous unrealized loss position as of December 31, 2018 and 2017 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, 2018
Corporate debt	$	80,282	$	(256	)	$	87,028	$	(782	)	$	167,310	$	(1,038	)
As of December 31, 2017
Corporate debt	$	177,114	$	(536	)	$	26,476	$	(253	)	$	203,590	$	(789	)