4. Marketable Securities

The following is a summary of marketable securities designated as available-for-sale as of December 31, 2013:

			Gross		Gross
	Amortized		Unrealized		Unrealized			Estimated
	Cost		Gains		Losses			Fair Value
Corporate bonds	$	37,399	$	1	$	(29	)	$	37,371
Municipal bonds		10,820		2		(3	)		10,819
Certificates of deposit		498		-		-			498
Total marketable securities	$	48,717	$	3	$	(32	)	$	48,688

All marketable securities are classified as current regardless of contractual maturity dates because we consider such investments to represent cash available for current operations.

As of December 31, 2013, we did not consider any of our marketable securities to be other-than-temporarily impaired. When evaluating our investments for other-than-temporary impairment, we review factors such as the length of time and extent to which fair value has been below its cost basis, the financial condition of the issuer, our ability and intent to hold the security and whether it is more likely than not that we will be required to sell the investment before recovery of its cost basis.

The following is a summary of amortized cost and estimated fair value of marketable securities as of December 31, 2013, by maturity:

			Gross		Gross
	Amortized		Unrealized		Unrealized			Estimated
	Cost		Gains		Losses			Fair Value
Due in one year or less	$	47,398	$	3	$	(32	)	$	47,369
Due after one year		1,319		-		-			1,319
Total marketable securities	$	48,717	$	3	$	(32	)	$	48,688

We did not hold any marketable securities as of December 31, 2012.