Fair Value Measurements

The following is a summary of available-for-sale marketable securities held as of December 31, 2015 and 2014 (in thousands):



			Gross Unrealized					Aggregate Fair Value		Classification on Balance Sheet
	Amortized Cost									Short-Term Marketable Securities		Long-Term Marketable Securities
As of December 31, 2015	Amortized Cost		Gains		Losses					Short-Term Marketable Securities		Long-Term Marketable Securities
Commercial paper	$	2,491	$	—	$	(4	)	$	2,487	$	2,487	$	—
Corporate bonds	995,100		73		(3,365		)	991,808		432,585		559,223
U.S. government agency obligations	239,587		41		(575		)	239,053		25,016		214,037
	$	1,237,178	$	114	$	(3,944	)	$	1,233,348	$	460,088	$	773,260

As of December 31, 2014
Certificates of deposit	$	39	$	—	$	—		$	39	$	—	$	39
Commercial paper	10,487		—		(2		)	10,485		10,485		—
Corporate bonds	1,077,387		454		(2,132		)	1,075,709		424,777		650,932
U.S. government agency obligations	303,808		20		(427		)	303,401		84,380		219,021
	$	1,391,721	$	474	$	(2,561	)	$	1,389,634	$	519,642	$	869,992

During the first quarter of 2015, the Company began offering eligible employees the ability to participate in a non-qualified deferred compensation plan. The mutual funds held by the Company that are associated with this plan are classified as restricted trading securities. These securities are not included in the available-for-sale securities table above but are included in marketable securities in the consolidated balance sheets.

Unrealized gains and unrealized temporary losses on investments classified as available-for-sale are included within accumulated other comprehensive loss in the consolidated balance sheets. Upon realization, those amounts are reclassified from accumulated other comprehensive loss to interest income in the consolidated statements of income. As of December 31, 2015, the Company held for investment corporate bonds with a fair value of $71.4 million, which are classified as available-for-sale marketable securities and have been in a continuous unrealized loss position for more than 12 months. The unrealized losses are not significant and are attributable to changes in interest rates. The Company does not believe any unrealized losses represent other than temporary impairments based on the evaluation of available evidence. As of December 31, 2014, there were no securities in a continuous unrealized loss position for more than 12 months.

The following table details the fair value measurements within the fair value hierarchy of the Company’s financial assets and liabilities as of December 31, 2015 and 2014 (in thousands):



	Total Fair Value			Fair Value Measurements at Reporting Date Using
	Total Fair Value			Level 1		Level 2		Level 3
As of December 31, 2015
Cash Equivalents and Marketable Securities:
Money market funds	$	1,250		$	1,250	$	—	$	—
Commercial paper	2,487			—		2,487		—
Corporate bonds	991,808			—		991,808		—
U.S. government agency obligations	239,053			—		239,053		—
Mutual funds	1,414			1,414		—		—
	$	1,236,012		$	2,664	$	1,233,348	$	—

As of December 31, 2014
Cash Equivalents and Marketable Securities:
Money market funds	$	501		$	501	$	—	$	—
Certificates of deposit	39			39		—		—
Commercial paper	10,485			—		10,485		—
Corporate bonds	1,075,709			—		1,075,709		—
U.S. government agency obligations	303,401			—		303,401		—
	$	1,390,135		$	540	$	1,389,595	$	—

Other Liabilities:
Contingent consideration obligation related to Velocius acquisition	$	(900	)	$	—	$	—	$	(900	)

The following table reflects the activity for the Company’s major classes of assets and liabilities measured at fair value using Level 3 inputs for the years ended December 31, 2015 and 2014 (in thousands):



	Other Assets: Note Receivable			Other Liabilities: Contingent Consideration Obligation
Balance, January 1, 2014	$	22,879		$	(2,600	)
Fair value adjustment to Velocius contingent consideration included in general and administrative expense	—			(300		)
Achievement of first milestone related to Velocius contingent consideration	—			2,000
Unrealized gain on convertible note receivable included in other comprehensive income	2,121			—
Amendment of the convertible note receivable for preferred stock of the issuer and cash	(25,000		)	—
Balance, December 31, 2014	$	—		$	(900	)
Fair value adjustment to Velocius contingent consideration included in general and administrative expense	—			(100		)
Achievement of final milestone related to Velocius contingent consideration	—			1,000
Balance, December 31, 2015	$	—		$	—

As of December 31, 2015 and 2014, the Company grouped money market funds, certificates of deposit, and mutual funds using a Level 1 valuation because market prices for such investments are readily available in active markets. As of December 31, 2015 and 2014, the Company grouped commercial paper, U.S. government agency obligations and corporate bonds using a Level 2 valuation because quoted prices for identical or similar assets are available in markets that are inactive. The Company did not have any transfers of assets and liabilities between Level 1 and Level 2 of the fair value measurement hierarchy during the years ended December 31, 2015 and 2014.

When developing fair value estimates, the Company maximizes the use of observable inputs and minimizes the use of unobservable inputs. When available, the Company uses quoted market prices to measure fair value. The valuation technique used to measure fair value for the Company's Level 1 and Level 2 assets is a market approach, using prices and other relevant information generated by market transactions involving identical or comparable assets. If market prices are not available, the fair value measurement is based on models that use primarily market-based parameters including yield curves, volatilities, credit ratings and currency rates. In certain cases where market rate assumptions are not available, the Company is required to make judgments about assumptions market participants would use to estimate the fair value of a financial instrument.

The valuation technique used to measure the fair value of a Level 3 asset held by the Company, which consisted of a $25.0 million face value convertible note receivable, was primarily an income approach, where the expected weighted average future cash flows were discounted back to present value. The significant unobservable inputs used in the fair value measurement of the convertible note receivable were the probability of conversion to equity and the fair value of equity into which the note was convertible. In the second quarter of 2014, the note was amended. Under the terms of the amendment, the note became convertible into shares of preferred stock of the issuer valued at $12.5 million at the time of conversion; the remaining $12.5 million was paid in cash in the second and third quarters of 2014.

The valuation technique used to measure fair value of the Company's Level 3 liability, which consisted of contingent consideration related to the acquisition of Velocius Networks, Inc. ("Velocius") in 2013 (Note 8), was primarily an income approach. The significant unobservable input used in the fair value measurement of the Velocius contingent consideration was the likelihood of achieving development milestones to integrate the acquired technology into the Company's technology. During the third quarter of 2014, the first of two milestones was achieved and a portion of the contingent consideration was paid. The remaining milestone was achieved in June 2015 and was paid in the third quarter of 2015.

Contractual maturities of the Company’s available-for-sale marketable securities held as of December 31, 2015 and 2014 were as follows (in thousands):



	December 31, 2015		December 31, 2014
Due in 1 year or less	$	460,088	$	519,642
Due after 1 year through 5 years	773,260		869,992
	$	1,233,348	$	1,389,634