Financial Instruments

6 Months Ended

12 Months Ended

Jun. 30, 2013

Dec. 31, 2012

Financial Instruments

4. Financial Instruments

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

	December 31, 2012						June 30, 2013
	Cost		Unrealized Gain (Loss)		Estimated Fair Value		Cost		Unrealized Gain (Loss)			Estimated Fair Value
Money market funds	$	43,303	$	–	$	43,303	$	103,302	$	–		$	103,302
Corporate notes and commercial paper		64,403		22		64,425		77,020		(16	)		77,004
U.S. government agency securities		19,335		11		19,346		45,960		(20	)		45,940
	$	127,041	$	33	$	127,074	$	226,282	$	(36)		$	226,246
Classified as:
Cash equivalents					$	43,303						$	103,302
Short-term investments						77,656							95,358
Long-term investments						6,115							27,586
Total cash equivalents and investments					$	127,074						$	226,246

At June 30, 2013 and December 31, 2012, the remaining contractual maturities of available-for-sale securities were less than two years. There have been no significant realized gains or losses on available-for-sale securities for the periods presented.

4. Financial Instruments

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, 2011							December 31, 2012
	Cost		Unrealized Gain (Loss)			Estimated Fair Value		Cost		Unrealized Gain		Estimated Fair Value
Money market funds	$	166,696	$	–		$	166,696	$	43,303	$	–	$	43,303
Corporate notes and commercial paper		9,895		(2	)		9,893		64,403		22		64,425
U.S. government agency securities		7,872		1			7,873		19,335		11		19,346
	$	184,463	$	(1	)	$	184,462	$	127,041	$	33	$	127,074

At December 31, 2012, the remaining contractual maturities of available-for-sale securities were less than two years. There have been no significant realized gains or losses on available-for-sale securities for the periods presented.