Cash and Cash Equivalents and Investments

6 Months Ended

Jun. 30, 2016

Cash and Cash Equivalents and Investments [Abstract]

Cash and Cash Equivalents Disclosure

Cash and Cash Equivalents and Investments

The fair value of cash and cash equivalents and investments held at June 30, 2016 and December 31, 2015 are as follows:

	As of June 30, 2016
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
	(in thousands)
Cash and cash equivalents	$	38,410	$	—	$	—		$	38,410
Securities maturing within one year:
U.S. treasury securities	379,307		333		—			379,640
Corporate debt securities	11,312		6		(3		)	11,315
Total short-term investments	$	390,619	$	339	$	(3	)	$	390,955
Total cash and cash equivalents and investments	$	429,029	$	339	$	(3	)	$	429,365
	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

There were no realized gains or losses for the six months ended June 30, 2016, and no realized gains or losses for the six months ended June 30, 2015. The cost of securities sold is based on the specific identification method.