3. Fair Value of Financial Instruments

The Company measures certain financial assets at fair value. Fair value is determined based upon the exit price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants, as determined by either the principal market or the most advantageous market. Inputs used in the valuation techniques to derive fair values are classified based on a three-level hierarchy, as follows:

•

Level 1 — Quoted prices in active markets for identical assets or liabilities.

•

Level 2 — Observable inputs other than Level 1 prices such as quoted prices for similar assets or liabilities; quoted prices in markets with insufficient volume or infrequent transactions (less active markets); or model-derived valuations in which all significant inputs are observable or can be derived principally from or corroborated by observable market data for substantially the full term of the assets or liabilities.

•

Level 3 — Unobservable inputs to the valuation methodology that are significant to the measurement of fair value of assets or liabilities.

The following table details the fair value measurements within the fair value hierarchy of the Company’s financial assets and liabilities at September 30, 2017 and December 31, 2016.

	September 30, 2017
	Level 1		Level 2		Level 3		Total
	(in thousands)
Cash equivalents and investments:
Money market funds	$	26,230	$	—	$	—	$	26,230
Commercial paper		—		4,767		—		4,767
Corporate bonds		—		77,359		—		77,359
U.S. government agency obligations		—		8,990		—		8,990
U.S. Treasury securities		—		368,422		—		368,422
Restricted cash:
Certificates of deposit		—		5,106		—		5,106
Other assets:
Strategic investments		—		—		2,800		2,800
Total	$	26,230	$	464,644	$	2,800	$	493,674

	December 31, 2016
	Level 1		Level 2		Level 3		Total
	(in thousands)
Cash equivalents and investments:
Money market funds	$	32,260	$	—	$	—	$	32,260
Commercial paper		—		12,439		—		12,439
Corporate bonds		—		66,947		—		66,947
U.S. government agency obligations		—		10,980		—		10,980
Total	$	32,260	$	90,366	$	—	$	122,626

The Company considers all highly liquid investments purchased with a remaining maturity of three months or less to be cash equivalents. The fair value of the Company’s investments in certain money market funds is their face value and such instruments are classified as Level 1 and are included in cash and cash equivalents on the consolidated balance sheets. At September 30, 2017 and December 31, 2016, our Level 2 securities were priced by pricing vendors. These pricing vendors utilize the most recent observable market information in pricing these securities or, if specific prices are not available for these securities, use other observable inputs like market transactions involving identical or comparable securities.

As of September 30, 2017, the fair value of the 2022 Notes (Note 7) was $443.6 million. The fair value was determined on the basis of market prices observable for similar instruments and is considered Level 2 in the fair value hierarchy.

For certain other financial instruments, including accounts receivable, accounts payable, capital leases and other current liabilities, the carrying amounts approximate their fair value due to the relatively short maturity of these balances.

Restricted cash is comprised of certificates of deposit related to landlord guarantees for our leased facilities. These restricted cash balances have been excluded from our cash and cash equivalents balance on our consolidated balance sheets.

Strategic investments consist of non-controlling equity investments in privately held companies. These investments without readily determinable fair values for which the Company does not have the ability to exercise significant influence are accounted for using the cost method of accounting. Under the cost method of accounting, the non-marketable securities are carried at cost and are adjusted only for other-than-temporary impairments, certain distributions and additional investments. These investments are valued using significant unobservable inputs or data in an inactive market and the valuation requires the Company's judgment due to the absence of market prices and inherent lack of liquidity. The estimated fair value is based on quantitative and qualitative factors including, but not limited to, subsequent financing activities by the investee and projected discounted cash flows. Fair value is not estimated for non-marketable equity securities if there are no identified events or changes in circumstances that may have an effect on the fair value of the investment.

The following tables summarize the composition of our short- and long-term investments at September 30, 2017 and December 31, 2016.

	September 30, 2017
	Amortized Cost		Unrealized Gains		Unrealized Losses			Aggregate Fair Value
	(in thousands)
Commercial paper	$	4,770	$	—	$	(3	)	$	4,767
Corporate bonds		77,460		2		(103	)		77,359
U.S. government agency obligations		8,999		—		(9	)		8,990
U.S. Treasury securities		259,663		26		(6	)		259,683
Total	$	350,892	$	28	$	(121	)	$	350,799

	December 31, 2016
	Amortized Cost		Unrealized Gains		Unrealized Losses			Aggregate Fair Value
	(in thousands)
Commercial paper	$	12,446	$	—	$	(7	)	$	12,439
Corporate bonds		67,126		—		(179	)		66,947
U.S. government agency obligations		10,998		—		(18	)		10,980
Total	$	90,570	$	—	$	(204	)	$	90,366

For all of our securities for which the amortized cost basis was greater than the fair value at September 30, 2017, the Company has concluded that there is no plan to sell the security nor is it more likely than not that the Company would be required to sell the security before its anticipated recovery. In making the determination as to whether the unrealized loss is other-than-temporary, the Company considered the length of time and extent the investment has been in an unrealized loss position, the financial condition and near-term prospects of the issuers, the issuers’ credit rating and the time to maturity.

Contractual Maturities

The contractual maturities of short-term and long-term investments held at September 30, 2017 and December 31, 2016 are as follows:

	September 30, 2017				December 31, 2016
	Amortized Cost Basis		Aggregate Fair Value		Amortized Cost Basis		Aggregate Fair Value
	(in thousands)				(in thousands)
Due within one year	$	315,178	$	315,130	$	54,694	$	54,648
Due after 1 year through 2 years		35,714		35,669		35,876		35,718
Total	$	350,892	$	350,799	$	90,570	$	90,366