Cash and Cash Equivalents and Investments

12 Months Ended

Dec. 31, 2015

Cash and Cash Equivalents and Investments [Abstract]

Cash and Cash Equivalents and Investments

Cash and Cash Equivalents and Investments

The fair value of cash and cash equivalents and investments held at December 31, 2015 and 2014 are as follows:

	As of December 31, 2015
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
			(in thousands)
Cash and cash equivalents	$	202,989	$	—	$	—		$	202,989
Securities maturing within one year:
U.S. treasury securities	313,105		2		(219		)	312,888
Corporate debt securities	5,477		—		(2		)	5,475
Total short-term investments	$	318,582	$	2	$	(221	)	$	318,363
Total cash and cash equivalents and investments	$	521,571	$	2	$	(221	)	$	521,352

	As of December 31, 2014
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
			(in thousands)
Cash and cash equivalents	$	137,266	$	—	$	—		$	137,266
Securities maturing within one year:
Certificates of deposit	552		—		—			552
U.S. treasury securities	201,584		3		(66		)	201,521
Total short-term investments	$	202,136	$	3	$	(66	)	$	202,073
Total cash and cash equivalents and investments	$	339,402	$	3	$	(66	)	$	339,339

There were no realized gains or losses for the year ended December 31, 2015, no realized gains or losses for the year ended December 31, 2014, and no realized gains or losses for the year ended December 31, 2013.