At December 31, 2015, marketable securities by security type consisted of:

 

		Amortized Cost				Gross Unrealized Gains				Gross Unrealized Losses				Estimated Fair Value
United States treasury notes		$	44,587			$	—			$	(53	)		$	44,534
Agency bonds			29,761				—				(15	)			29,746
Total		$	74,348			$	—			$	(68	)		$	74,280

 

At December 31, 2014, marketable securities by security type consisted of:

 

		Amortized Cost				Gross Unrealized Gains				Gross Unrealized Losses				Estimated Fair Value
United States treasury notes		$	10,026			$	—			$	—			$	10,026
Agency bonds			27,409				—				—				27,409
Total		$	37,435			$	—			$	—			$	37,435