Financial Instruments

3 Months Ended

Mar. 31, 2016

Investments Debt And Equity Securities [Abstract]

Financial Instruments

4. Financial Instruments

Cash equivalents and investments, all of which are classified as available-for-sale securities, consisted of the following (in thousands):

	March 31, 2016									December 31, 2015
								Estimated									Estimated
			Unrealized		Unrealized			Fair				Unrealized		Unrealized			Fair
	Cost		Gain		(Loss)			Value		Cost		Gain		(Loss)			Value
Money market funds	$	29,876	$	—	$	—		$	29,876	$	22,074	$	—	$	—		$	22,074
Corporate notes and commercial paper		217,955		19		(3	)		217,971		242,089		3		(59	)		242,033
U.S. government agency securities		127,555		57		(7	)		127,605		180,970		1		(95	)		180,876
	$	375,386	$	76	$	(10	)	$	375,452	$	445,133	$	4	$	(154	)	$	444,983
Classified as:
Cash equivalents								$	165,177								$	171,310
Short-term investments									210,275									257,713
Long-term investments									—									15,960
Total cash equivalents and    investments								$	375,452								$	444,983

At March 31, 2016, the remaining contractual maturities of available-for-sale securities were less than one year and at December 31, 2015 the remaining contractual maturities of available-for-sale securities were less than two years. There have been no significant realized gains or losses on available-for-sale securities for the periods presented.