3. Cash, cash equivalents and marketable securities

The following is a summary of cash, cash equivalents and marketable securities available-for-sale as of September 30, 2013 and December 31, 2012 (in thousands):

	Amortized Cost
September 30, 2013
Cash and cash equivalents:
Cash	$	2,093	$	—	$	—		$	2,093
Money market funds		9,598		—		—			9,598
U.S. government agency securities		500		—		—			500
Total cash and cash equivalents		12,191		—		—			12,191
Marketable securities available-for-sale:
U.S. treasury securities		2,500		—		—			2,500
U.S. government agency securities		61,761		22		—			61,783
Total marketable securities available-for-sale		64,261		22		—			64,283
Total cash, cash equivalents and marketable securities	$	76,452	$	22	$	—		$	76,474
December 31, 2012
Cash and cash equivalents:
Cash	$	1,542	$	—	$	—		$	1,542
Money market funds		3,140		—		—			3,140
Municipal securities		2,202		—		—			2,202
U.S. government agency securities		715		—		—			715
Total cash and cash equivalents		7,599		—		—			7,599
Marketable securities available-for-sale:
U.S. government agency securities		116,986		46		(1	)		117,031
U.S. treasury securities		500		—		—			500
Total marketable securities available-for-sale		117,486		46		(1	)		117,531
Total cash, cash equivalents and marketable securities	$	125,085	$	46	$	(1	)	$	125,130

The following is a summary of the amortized cost and estimated fair value of marketable securities available-for-sale, by contractual maturity (in thousands):

	September 30, 2013
	Amortized Cost		Estimated Fair Value
Mature in one year or less	$	55,761	$	55,778
Mature after one year through two years		8,500		8,505
	$	64,261	$	64,283

We have classified our entire investment portfolio as available-for-sale. We view our available-for-sale portfolio as available for use in current operations and accordingly have classified all investments as short-term. Available-for-sale securities are carried at fair value based on inputs that are observable, either directly or indirectly, such as quoted market prices for similar securities; quoted prices in markets that are not active; or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the securities with unrealized gains and losses included in accumulated other comprehensive income (loss) in stockholders’ equity. Realized gains and losses and declines in value, if any, judged to be other than temporary on available-for-sale securities are included in interest income or expense. The cost of securities sold is based on the specific identification method. Management assesses whether declines in the fair value of investment securities are other than temporary. In determining whether a decline is other than temporary, management considers the following factors:

Whether the investment has been in a continuous realized loss position for over 12 months;
the duration to maturity of our investments;
our intention to hold the investments to maturity and if it is not more likely than not that we will be required to sell the investment before recovery of the amortized cost basis;
the credit rating, financial condition and near-term prospects of the issuer; and
the type of investments made.

To date, there have been no declines in fair value that have been identified as other than temporary.