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 September 30, 2014 (amounts in thousands):



	Available-for-sale Securities
	Adjusted Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Government agency bonds	$	668,639	$	129	$	(2,560	)	$	666,208
Municipal bonds	41,097		66		(2		)	41,161
Auction rate securities	9,825		—		—			9,825
Time deposits (1)	20,160		—		—			20,160
Corporate bonds and debt	904,243		2,150		(800		)	905,593
	$	1,643,964	$	2,345	$	(3,362	)	$	1,642,947

(1) Time deposits in various financial institutions with maturities greater than three months that will mature within one year.

The following is a summary of available-for-sale securities at March 31, 2014 (amounts in thousands):



	Available-for-sale Securities
	Adjusted Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Government agency bonds	$	684,451	$	114	$	(3,171	)	$	681,394
Municipal bonds	41,622		101		(14		)	41,709
Auction rate securities	9,825		—		—			9,825
Corporate bonds and debt	941,524		3,247		(805		)	943,966
	$	1,677,422	$	3,462	$	(3,990	)	$	1,676,894

At September 30, 2014, the Company's available-for-sale debt securities are presented on the condensed consolidated balance sheets as short-term investments of $801.7 million and long-term investments of $841.3 million. At March 31, 2014, the Company's available-for-sale debt securities are presented on the condensed consolidated balance sheets as short-term investments of $878.2 million and long-term investments of $798.7 million.

At September 30, 2014, the Company evaluated its investment portfolio and noted unrealized losses of $3.4 million on its debt securities with an aggregated fair value of $833.3 million, 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 September 30, 2014 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 September 30, 2015, 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 September 30, 2014, 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	$	250,615	$	742	$	(5	)	$	251,352
Due after one year and through five years	1,264,898		1,552		(2,227		)	1,264,223
Due after five years and through ten years	112,436		51		(1,130		)	111,357
Due after ten years	9,825		—		—			9,825
	$	1,637,774	$	2,345	$	(3,362	)	$	1,636,757

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 six-month periods ended September 30, 2014 and 2013.