Financial Instruments (Tables)

6 Months Ended

Jun. 30, 2014

Cash Equivalents and Investments Classified as Available-for-sale Securities

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

	June 30, 2014									December 31, 2013
								Estimated									Estimated
			Unrealized		Unrealized			Fair				Unrealized		Unrealized			Fair
	Cost		Gain		(Loss)			Value		Cost		Gain		(Loss)			Value
Money market funds	$	6,692	$	—	$	—		$	6,692	$	57,296	$	—	$	—		$	57,296
Corporate notes and commercial paper		191,153		48		(43	)		191,158		182,426		62		(16	)		182,472
U.S. government agency securities		67,051		21		(4	)		67,068		75,278		23		(12	)		75,289
	$	264,896	$	69	$	(47	)	$	264,918	$	315,000	$	85	$	(28	)	$	315,057
Classified as:
Cash equivalents								$	36,059								$	113,794
Short-term investments									170,857									150,892
Long-term investments									58,002									50,371
Total cash equivalents and investments								$	264,918								$	315,057