Investments

The Company's investments are intended to establish a high-quality portfolio that preserves principal, meets liquidity needs, avoids inappropriate concentrations, and delivers an appropriate yield in relationship to the Company's investment guidelines and market conditions. The following is a summary of available-for-sale securities at December 31, 2013 (amounts in thousands):



	Available-for-sale Securities
	Adjusted Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Government agency bonds	$	741,492	$	164	$	(5,645	)	$	736,011
Municipal bonds	51,940		20		(209		)	51,751
Auction rate securities	9,827		—		—			9,827
Corporate bonds and debt	857,038		2,858		(1,258		)	858,638
	$	1,660,297	$	3,042	$	(7,112	)	$	1,656,227

The following is a summary of available-for-sale and marketable equity securities at March 31, 2013 (amounts in thousands):



	Available-for-sale Securities
	Adjusted Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Government agency bonds	$	558,116	$	335	$	(298	)	$	558,153
Municipal bonds	25,000		146		(8		)	25,138
Auction rate securities	33,459		332		—			33,791
Corporate bonds and debt	680,144		5,137		(159		)	685,122
Marketable equity securities	5,270		239		—			5,509
	$	1,301,989	$	6,189	$	(465	)	$	1,307,713

At December 31, 2013, the Company's available-for-sale debt securities are presented on the condensed consolidated balance sheets as short-term investments of $932.3 million and long-term investments of $723.9 million. At March 31, 2013, the Company’s available-for-sale debt securities and marketable equity securities are presented on the condensed consolidated balance sheets as short-term investments of $1,050.3 million and long-term investments of $257.5 million.

At December 31, 2013, the Company evaluated its investment portfolio and noted unrealized losses of $7.1 million on its debt securities which were due primarily to higher interest rates and resulting declines in market prices. Management does not believe any of the unrealized losses represent an other-than-temporary impairment based on its evaluation of available evidence as of December 31, 2013 and the Company's intent is to hold these investments until these assets are no longer impaired, except for certain auction rate securities (ARS). For those debt securities not scheduled to mature until after December 31, 2014, such recovery is not anticipated to occur in the next year and these investments have been classified as long-term investments.

The amortized cost and estimated fair value of the available-for-sale securities at December 31, 2013, by contractual maturity, excluding corporate debt of $6.2 million, which has no contractual maturity, are shown below (amounts in thousands). Expected maturities can differ from contractual maturities because the issuers of the securities may have the right to prepay obligations without prepayment penalties, and the Company views its available-for-sale securities as available for current operations.



	Adjusted Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Available-for-sale
Due in one year or less	$	190,841	$	721	$	—		$	191,562
Due after one year and through five years	1,332,690		2,321		(2,223		)	1,332,788
Due after five years and through ten years	120,749		—		(4,889		)	115,860
Due after ten years	9,827		—		—			9,827
	$	1,654,107	$	3,042	$	(7,112	)	$	1,650,037

The Company had no material realized gains or losses from the sale of available-for-sale marketable equity securities or debt securities during each of the three and nine-month periods ended December 31, 2013 and 2012.