4. Investments in Available-for-Sale Securities

The following is a summary of the Company’s investments in available-for-sale securities as of March 31, 2012:

	Cost		Unrealized Gains		Unrealized Losses			Fair Value
U.S. federal agency securities	$	15,122	$	335	$	-		$	15,457
Certificates of deposit		1,604,262		9,810		(10,683	)		1,603,389
Corporate debt securities		711,152		1,429		(24,776	)		687,805
	$	2,330,536	$	11,574	$	(35,459	)	$	2,306,651

The following is a summary of the Company’s investments in available-for-sale securities as of December 31, 2011:

	Cost		Unrealized Gains		Unrealized Losses			Fair Value
U.S. federal agency securities	$	15,153	$	411	$	-		$	15,564
Certificates of deposit		1,725,402		11,154		(13,970	)		1,722,586
Corporate debt securities		776,244		1,222		(23,843	)		753,623
	$	2,516,799	$	12,787	$	(37,813	)	$	2,491,773

The Company’s investment portfolio had a gross realized loss of $1,801 and a gain of $2,404 for the three months ended March 31, 2012 and 2011, respectively.

The cost and fair value of investments in available-for-sale securities, by contractual maturity, as of March 31, 2012, were as follows:

	Cost		Fair Value
Due within one year	$	1,750,030	$	1,731,553
Due after one year through three years		466,842		458,244
Due after three years		113,664		116,854
	$	2,330,536	$	2,306,651

Expected maturities will differ from contractual maturities because the issuers of certain debt securities have the right to call or prepay their obligations without any penalties. Accordingly, the Company has classified the entire fair value of its investments in available-for-sale securities as current assets in the accompanying balance sheets.