The following is a summary of our investments as of September 30, 2013 and December 31, 2012 (in thousands):

	September 30, 2013
			Gross		Gross			Estimated
	Amortized		Unrealized		Unrealized			Fair
	Cost		Gains		Losses			Value
Corporate debt securities
Due in one year or less	$	45,645	$	67	$	(2	)	$	45,710
Due in one to three years	84,020		92		(158		)	83,954
U.S. treasury and government agency securities
Due in one year or less	22,551		25		—			22,576
Due in one to three years	30,321		53		(19		)	30,355
Total investments	$	182,537	$	237	$	(179	)	$	182,595

	December 31, 2012
			Gross		Gross			Estimated
	Amortized		Unrealized		Unrealized			Fair
	Cost		Gains		Losses			Value
Corporate debt securities
Due in one year or less	$	52,332	$	88	$	(6	)	$	52,414
Due in one to three years	59,176		137		(37		)	59,276
U.S. treasury and government agency securities
Due in one year or less	24,795		86		—			24,881
Due in one to three years	34,606		84		(2		)	34,688
Commercial paper
Due in one year or less	9,494		1		(4		)	9,491
Total investments	$	180,403	$	396	$	(49	)	$	180,750