(5) FAIR VALUE MEASUREMENTS

The Financial Accounting Standards Board has issued authoritative guidance which requires that fair value should be based on the assumptions market participants would use when pricing an asset or liability and establishes a fair value hierarchy that prioritizes the information used to develop those assumptions. Under the standard, fair value measurements are separately disclosed by level within the fair value hierarchy. The fair value hierarchy establishes and prioritizes the inputs used to measure fair value that maximizes the use of observable inputs and minimizes the use of unobservable inputs. Observable inputs are inputs that reflect the assumptions that market participants would use in pricing the asset or liability developed based on market data obtained from sources independent of the Company. Unobservable inputs are inputs that reflect the Company’s assumptions about the assumptions market participants would use in pricing the asset or liability developed based on the best information available in the circumstances.

The three levels of the fair value hierarchy established are as follows:


Level 1		Quoted prices (unadjusted) in active markets for identical assets or liabilities that the Company has the ability to access as of the reporting date. Active markets are those in which transactions for the asset or liability occur in sufficient frequency and volume to provide pricing information on an ongoing basis.

Level 2		Pricing inputs other than quoted prices in active markets included in Level 1, which are either directly or indirectly observable as of the reporting date. These include quoted prices for similar assets or liabilities in active markets and quoted prices for identical or similar assets or liabilities in markets that are not active.

Level 3		Unobservable inputs that reflect the Company’s assumptions about the assumptions that market participants would use in pricing the asset or liability. Unobservable inputs shall be used to measure fair value to the extent that observable inputs are not available.

Fixed-income securities and mutual funds are valued using a third-party pricing agency. The valuation is based on observable inputs including pricing for similar assets and other observable market factors. There has been no material change from period to period. The estimated fair value of the Company’s long-term debt based on a market approach was approximately $4.4 million and $4.5 million as of March 31, 2018 and December 31, 2017, respectively, and represent Level 2 measurements. When determining the estimated fair value of the Company’s long-term debt, the Company used market-based risk measurements, such as credit risk.

The following table presents the Company’s fair value measurements as of March 31, 2018 along with the level within the fair value hierarchy in which the fair value measurements in their entirety fall.


			Fair Value Measurement at March 31, 2018 Using:
			Quoted Prices		Significant
			in Active		Other		Significant
			Markets for		Observable		Unobservable
	Fair Value at		Identical Assets		Inputs		Inputs
(In thousands)	March 31, 2018		(Level 1)		(Level 2)		(Level 3)
Cash and cash equivalents
Cash and money market	$	101,103	$	101,103	$	—	$	—
Certificates of deposit		25,198		—		25,198		—
Commercial paper		11,998		—		11,998		—
U.S. government agency securities		8,398		—		8,398		—
Corporate bonds		1,998		—		1,998		—
Available-for-sale
Marketable securities
Corporate bonds		345,123		—		345,123		—
Asset backed securities		253,547		—		253,547		—
U.S. government agency securities		194,024		—		194,024		—
Commercial paper		51,994		—		51,994		—
Certificates of deposit		48,786		—		48,786		—
Total	$	1,042,169	$	101,103	$	941,066	$	—

The following table presents the Company’s fair value measurements as of December 31, 2017 along with the level within the fair value hierarchy in which the fair value measurements in their entirety fall.


			Fair Value Measurement at December 31, 2017 Using:
			Quoted Prices		Significant
			in Active		Other		Significant
			Markets for		Observable		Unobservable
	Fair Value at		Identical Assets		Inputs		Inputs
(In thousands)	December 31, 2017		(Level 1)		(Level 2)		(Level 3)
Cash and cash equivalents
Cash and money market	$	61,297	$	61,297	$	—	$	—
Commercial paper		10,995				10,995		—
Certificates of deposit		1,499				1,499		—
U.S. government agency securities		3,700				3,700		—
Available-for-sale
Marketable securities
Corporate bonds		181,305		—		181,305		—
Asset backed securities		94,515		—		94,515		—
U.S. government agency securities		54,812		—		54,812		—
Commercial paper		9,946		—		9,946		—
Certificates of deposit		6,646		—		6,646		—
Total	$	424,715	$	61,297	$	363,418	$	—

The Company monitors investments for other-than-temporary impairment. It was determined that unrealized gains and losses as of March 31, 2018 and December 31, 2017 are temporary in nature because the change in market value for those securities has resulted from fluctuating interest rates rather than a deterioration of the credit worthiness of the issuers. So long as the Company holds these securities to maturity, it is unlikely to experience gains or losses. In the event that the Company disposes of these securities before maturity, it is expected that realized gains or losses, if any, will be immaterial.

The following table summarizes gross unrealized losses and fair values of our investments in an unrealized loss position as of March 31, 2018, aggregated by investment category and length of time that individual securities have been in a continuous unrealized loss position:


		March 31, 2018
		Less than 12 months			12 months or greater				Total
(In thousands)		Fair Value		Gross Unrealized Loss		Fair Value		Gross Unrealized Loss		Fair Value		Gross Unrealized Loss
Marketable securities
Corporate bonds	$	328,935	$	(1,073)	$	—	$	—	$	328,935	$	(1,073)
Asset backed securities		252,105		(841)		1,442		(2)		253,547		(843)
U.S. government agency securities		169,071		(237)		24,953		(46)		194,024		(283)
Commercial paper		51,425		(21)		—		—		51,425		(21)
Certificates of deposit		41,551		(79)		—		—		41,551		(79)
Total	$	843,087	$	(2,251)	$	26,395	$	(48)	$	869,482	$	(2,299)

The following summarizes contractual underlying maturities of the Company’s available-for-sale investments in debt securities at March 31, 2018:


		Due one year or less			Due after one year through four years
(In thousands)		Cost		Fair Value		Cost		Fair Value
Marketable securities
Corporate bonds	$	224,976	$	224,287	$	121,217	$	120,836
U.S. government agency securities		174,495		174,218		19,812		19,806
Commercial paper		52,015		51,994		—		—
Certificates of deposit		46,888		46,820		1,976		1,966
Asset backed securities		30,844		30,753		223,546		222,794
Total	$	529,218	$	528,072	$	366,551	$	365,402