Financial Instruments (Tables)

12 Months Ended

Dec. 31, 2014

Investments Debt And Equity Securities [Abstract]

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

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

	December 31, 2014									December 31, 2013
								Estimated									Estimated
			Unrealized		Unrealized			Fair				Unrealized		Unrealized			Fair
	Cost		Gains		(Losses)			Value		Cost		Gains		(Losses)			Value
Money market funds	$	24,915	$	–	$	–		$	24,915	$	57,296	$	–	$	–		$	57,296
Corporate notes and commercial paper		226,209		8		(170	)		226,047		182,426		62		(16	)		182,472
U.S. government agency securities		120,246		4		(81	)		120,169		75,278		23		(12	)		75,289
	$	371,370	$	12	$	(251	)	$	371,131	$	315,000	$	85	$	(28	)	$	315,057
Classified as:
Cash equivalents								$	36,341								$	113,794
Short-term investments									251,759									150,892
Long-term investments									83,030									50,371
Total cash equivalents and investments								$	371,131								$	315,057