Financial Instruments (Tables)

6 Months Ended

Jun. 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):

	June 30, 2015									December 31, 2014
								Estimated									Estimated
			Unrealized		Unrealized			Fair				Unrealized		Unrealized			Fair
	Cost		Gain		(Loss)			Value		Cost		Gain		(Loss)			Value
Money market funds	$	20,483	$	—	$	—		$	20,483	$	24,915	$	—	$	—		$	24,915
Corporate notes and commercial paper		214,666		5		(105	)		214,566		226,209		8		(170	)		226,047
U.S. government agency securities		155,796		26		(17	)		155,805		120,246		4		(81	)		120,169
	$	390,945	$	31	$	(122	)	$	390,854	$	371,370	$	12	$	(251	)	$	371,131
Classified as:
Cash equivalents								$	52,167								$	36,342
Short-term investments									332,596									251,759
Long-term investments									6,091									83,030
Total cash equivalents and investments								$	390,854								$	371,131