Financial Instruments (Tables)

9 Months Ended

Sep. 30, 2015

Investments Debt And Equity Securities [Abstract]

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):

	September 30, 2015									December 31, 2014
								Estimated									Estimated
			Unrealized		Unrealized			Fair				Unrealized		Unrealized			Fair
	Cost		Gain		(Loss)			Value		Cost		Gain		(Loss)			Value
Money market funds	$	21,351	$	—	$	—		$	21,351	$	24,915	$	—	$	—		$	24,915
Corporate notes and commercial paper		181,981		14		(33	)		181,962		226,209		8		(170	)		226,047
U.S. government agency securities		140,017		39		(1	)		140,056		120,246		4		(81	)		120,169
	$	343,349	$	53	$	(34	)	$	343,369	$	371,370	$	12	$	(251	)	$	371,131
Classified as:
Cash equivalents								$	65,123								$	36,342
Short-term investments									278,246									251,759
Long-term investments									—									83,030
Total cash equivalents and investments								$	343,369								$	371,131