Fair Value Measurements (Tables)

3 Months Ended

Mar. 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 March 31, 2018
Money market funds	$	61,139	$	—		$	—	$	61,139
Securities available-for-sale
Corporate debt		—		151,082			—		151,082
Trading securities
Corporate debt		—		88,861			—		88,861
Mutual funds held in rabbi trust		—		4,328			—		4,328
Foreign currency forward position		—		288			—		288
Total	$	61,139	$	244,559		$	—	$	305,698
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 Company’s foreign currency forward position is as follows:

	As of
	March 31, 2018		December 31, 2017
	(In thousands)
Notional value	$	88,190	$	84,422
Fair value of notional		87,902		85,124
Fair value of the asset (liability)	$	288	$	(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 March 31, 2018
Securities available-for-sale
Corporate debt	$	151,999	$	11	$	(928	)	$	151,082
Trading securities
Corporate debt		89,528		17		(684	)		88,861
Mutual funds held in rabbi trust		4,347		—		(19	)		4,328
Total trading securities		93,875		17		(703	)		93,189
Total investments	$	245,874	$	28	$	(1,631	)	$	244,271
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
	March 31, 2018		December 31, 2017
	(In thousands)
Less than one year	$	135,048	$	130,738
Due in 1 - 5 years		109,223		108,783
Total	$	244,271	$	239,521

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 March 31, 2018 and December 31, 2017:

	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 March 31, 2018
Corporate debt	$	175,135	$	(1,247	)	$	26,735	$	(365	)	$	201,870	$	(1,612	)
As of December 31, 2017
Corporate debt	$	177,114	$	(536	)	$	26,476	$	(253	)	$	203,590	$	(789	)