Financial Instruments (Tables)

12 Months Ended

Dec. 31, 2015

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, 2015									December 31, 2014
								Estimated									Estimated
			Unrealized		Unrealized			Fair				Unrealized		Unrealized			Fair
	Cost		Gains		(Losses)			Value		Cost		Gains		(Losses)			Value
Money market funds	$	22,074	$	–	$	–		$	22,074	$	24,915	$	–	$	–		$	24,915
Corporate notes and commercial paper		242,089		3		(59	)		242,033		226,209		8		(170	)		226,047
U.S. government agency securities		180,970		1		(95	)		180,876		120,246		4		(81	)		120,169
	$	445,133	$	4	$	(154	)	$	444,983	$	371,370	$	12	$	(251	)	$	371,131
Classified as:
Cash equivalents								$	171,310								$	36,341
Short-term investments									257,713									251,759
Long-term investments									15,960									83,030
Total cash equivalents and investments								$	444,983								$	371,131