4.	Cash, Cash Equivalents and Marketable Securities

Cash, cash equivalents and marketable securities consist of the following (in thousands):

	Amortized Cost		Unrealized Gains		Unrealized Losses			Estimated Fair Value
December 31, 2016
Cash and cash equivalents:
Cash	$	3,557	$	-	$	-		$	3,557
Money market funds		18,981		-		-			18,981
U.S. government agency securities		1,751		-		-			1,751
Total cash and cash equivalents		24,289		-		-			24,289
Marketable securities available-for-sale:
U.S. Treasuries		3,499		-		-			3,499
U.S. government agency securities		28,685		3		(2	)		28,686
Corporate debt securities		24,938		5		(2	)		24,941
Total marketable securities available-for-sale		57,122		8		(4	)		57,126
Total cash, cash equivalents and marketable securities	$	81,411	$	8	$	(4	)	$	81,415
December 31, 2015
Cash and cash equivalents:
Cash	$	4,561	$	-	$	-		$	4,561
Money market funds		21,193		-		-			21,193
Corporate debt securities		19,052		7		(1	)		19,058
Total cash and cash equivalents		44,806		7		(1	)		44,812
Marketable securities available-for-sale:
U.S. government agency securities		17,628		-		(6	)		17,622
Corporate debt securities		133,679		71		(59	)		133,691
Total marketable securities available-for-sale		151,307		71		(65	)		151,313
Total cash, cash equivalents and marketable securities	$	196,113	$	78	$	(66	)	$	196,125

The maturities of our marketable securities available-for-sale are as follows (in thousands):

	December 31, 2016
	Amortized Cost		Estimated Fair Value
Mature in one year or less	$	57,122	$	57,126
Mature after one year through two years		-		-
	$	57,122	$	57,126

There were no realized gains or losses from the sale of marketable securities in the years ended December 31, 2016, 2015 and 2014. All of our investments are classified as short-term and available-for-sale, as we consider them available to fund current operations and may not hold our investments until maturity.