Short-Term Marketable Securities (Tables)

12 Months Ended

Dec. 31, 2012

Short-Term Marketable Securities [Abstract]

Summary of short-term marketable securities

December 31, 2012	Amortized Cost		Unrealized Gain		Unrealized Loss		Market Value
U.S. treasuries	$	10,135	$	1	$	—	$	10,136
Government-sponsored enterprise securities		15,507		—		1		15,506
Corporate bonds		11,509		—		8		11,501
Certificate of deposit		496		—		—		496
	$	37,647	$	1	$	9	$	37,639
December 31, 2011	Amortized Cost		Unrealized Gain		Unrealized Loss		Market Value
U.S. treasuries	$	1,008	$	2	$	—	$	1,010
Government-sponsored enterprise securities		7,200		—		2		7,198
Certificate of deposit		525		—		—		525
	$	8,733	$	2	$	2	$	8,733