Investments

12 Months Ended

Dec. 31, 2018

Investments, Debt and Equity Securities [Abstract]

Investments

Investments

Our investments consisted of the following (in thousands):

	As of December 31, 2018
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value		Cash and Cash Equivalents		Short-Term Investments
Corporate notes and bonds	$	450,097	$	44	$	(1,818	)	$	448,323	$	—	$	448,323
U.S. Treasuries	112,783		2		(85		)	112,700		—		112,700
U.S. Government agencies	146,110		—		(442		)	145,668		—		145,668
Total	$	708,990	$	46	$	(2,345	)	$	706,691	$	—	$	706,691

	As of December 31, 2017
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value		Cash and Cash Equivalents		Short-Term Investments
Commercial paper	$	4,989	$	—	$	(2	)	$	4,987	$	—	$	4,987
Corporate notes and bonds	439,851		2		(1,829		)	438,024		—		438,024
U.S. Treasuries	3,098		—		—			3,098		3,098		—
U.S. Government agencies	273,950		—		(1,050		)	272,900		—		272,900
Total	$	721,888	$	2	$	(2,881	)	$	719,009	$	3,098	$	715,911

The following tables present the gross unrealized losses and related fair values of our investments that have been in a continuous unrealized loss position (in thousands):

	As of December 31, 2018
	Less Than 12 Months					Greater Than 12 Months					Total
	Fair Value		Unrealized Loss			Fair Value		Unrealized Loss			Fair Value		Unrealized Loss
Corporate notes and bonds	$	420,548	$	(1,817	)	$	1,526	$	(2	)	$	422,074	$	(1,819	)
U.S. Treasuries	105,525		(85		)	—		—			105,525		(85		)
U.S. Government agencies	137,416		(441		)	—		—			137,416		(441		)
Total	$	663,489	$	(2,343	)	$	1,526	$	(2	)	$	665,015	$	(2,345	)

	As of December 31, 2017
	Less Than 12 Months					Greater Than 12 Months					Total
	Fair Value		Unrealized Loss			Fair Value		Unrealized Loss			Fair Value		Unrealized Loss
Commercial paper	$	4,987	$	(2	)	$	—	$	—		$	4,987	$	(2	)
Corporate notes and bonds	284,499		(1,484		)	153,525		(345		)	438,024		(1,829		)
U.S. Treasuries	—		—			—		—			—		—
U.S. Government agencies	117,132		(486		)	155,768		(564		)	272,900		(1,050		)
Total	$	406,618	$	(1,972	)	$	309,293	$	(909	)	$	715,911	$	(2,881	)

Unrealized losses related to these investments are due to interest rate fluctuations as opposed to credit quality. In addition, we do not intend to sell, and it is not more likely than not that we would be required to sell, these investments before recovery of their cost basis. As a result, there is no other-than-temporary impairment for these investments as of December 31, 2018 and 2017.

The following table summarizes the contractual maturities of our investments at December 31, 2018 (in thousands):

	Amortized Cost		Fair Value
Due within one year	$	460,480	$	458,749
Due within one to three years	248,510		247,942
Total	$	708,990	$	706,691

All available-for-sale securities have been classified as current, based on management's intent and ability to use the funds in current operations.

As of December 31, 2018, we held a 11.1% ownership interest in a privately held company which is accounted for under the equity method based on our ability to exercise significant influence over the company's operating and financial policies. Our investments in this company are classified within deposits and other long-term assets on our consolidated balance sheets. The carrying value of our investments was $0.5 million and $2.1 million as of December 31, 2018 and 2017, respectively.