Cash, Cash Equivalents and Marketable Securities Available-for-Sale

6 Months Ended

Jun. 30, 2012

Cash, Cash Equivalents and Marketable Securities Available-for-Sale

Cash, Cash Equivalents and Marketable Securities Available-for-Sale

8.    Cash, Cash Equivalents and Marketable Securities Available-for-Sale

Money market funds of $667.3 million and $738.7 million at June 30, 2012 and December 31, 2011, respectively, were recorded at cost, which approximates fair value and are included in cash and cash equivalents.

The amortized cost, gross unrealized holding gains, gross unrealized holding losses and estimated fair value of available-for-sale securities by major security type and class of security at June 30, 2012 and December 31, 2011 were as follows:

			Gross		Gross		Estimated
	Amortized		Unrealized		Unrealized		Fair
June 30, 2012	Cost		Gain		Loss		Value
U.S. Treasury securities	$	418,287	$	20	$	(90)	$	418,217
U.S. government-sponsored agency securities	67,377		49		(4)		67,422
U.S. government-sponsored agency MBS	130,425		591		(636)		130,380
Non-U.S. government, agency and Supranational securities	2,668		24		-		2,692
Corporate debt - global	79,454		509		(41)		79,922
Marketable equity securities	407		25		-		432
Total available-for-sale marketable securities	$	698,618	$	1,218	$	(771)	$	699,065

			Gross		Gross		Estimated
	Amortized		Unrealized		Unrealized		Fair
December 31, 2011	Cost		Gain		Loss		Value
U.S. Treasury securities	$	228,996	$	58	$	(38)	$	229,016
U.S. government-sponsored agency securities	196,833		81		(69)		196,845
U.S. government-sponsored agency MBS	256,440		600		(1,901)		255,139
Non-U.S. government, agency and Supranational securities	2,666		19		-		2,685
Corporate debt - global	104,181		497		(233)		104,445
Marketable equity securities	407		153		-		560
Total available-for-sale marketable securities	$	789,523	$	1,408	$	(2,241)	$	788,690

U.S. government-sponsored agency securities include general unsecured obligations either issued directly by or guaranteed by U.S. Government Sponsored Enterprises.  U.S. government-sponsored agency mortgage-backed securities, or MBS, include mortgage-backed securities issued by the Federal National Mortgage Association, the Federal Home Loan Mortgage Corporation and the Government National Mortgage Association.  Non-U.S. government, agency and Supranational securities consist of direct obligations of highly rated governments of nations other than the United States and obligations of sponsored agencies and other entities that are guaranteed or supported by highly rated governments of nations other than the United States.  Corporate debt–global includes obligations issued by investment-grade corporations, including some issues that have been guaranteed by governments and government agencies.  Net unrealized gains in the marketable debt securities primarily reflect the impact of decreased interest rates at June 30, 2012.

Duration periods of available-for-sale debt securities at June 30, 2012 were as follows:

	Amortized		Fair
	Cost		Value
Duration of one year or less	$	200,221	$	200,280
Duration of one through three years	440,196		440,405
Duration of three through five years	57,794		57,948
Total	$	698,211	$	698,633