Financial Instruments (Tables)

3 Months Ended

Mar. 31, 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):

	March 31, 2015									December 31, 2014
								Estimated									Estimated
			Unrealized		Unrealized			Fair				Unrealized		Unrealized			Fair
	Cost		Gain		(Loss)			Value		Cost		Gain		(Loss)			Value
Money market funds	$	55,862	$	—	$	—		$	55,862	$	24,915	$	—	$	—		$	24,915
Corporate notes and commercial paper		255,007		23		(91	)		254,939		226,209		8		(170	)		226,047
U.S. government agency securities		131,711		16		(19	)		131,708		120,246		4		(81	)		120,169
	$	442,580	$	39	$	(110	)	$	442,509	$	371,370	$	12	$	(251	)	$	371,131
Classified as:
Cash equivalents								$	118,982								$	36,342
Short-term investments									258,567									251,759
Long-term investments									64,960									83,030
Total cash equivalents and investments								$	442,509								$	371,131