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, 2015 (amounts in thousands):



	Available-for-sale Securities
	Adjusted Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Government agency bonds	$	866,941	$	1,304	$	(51	)	$	868,194
Municipal bonds	42,579		11		(516		)	42,074
Auction rate securities	9,825		—		—			9,825
Corporate bonds and debt	1,127,390		1,323		(1,430		)	1,127,283
	$	2,046,735	$	2,638	$	(1,997	)	$	2,047,376

The following is a summary of available-for-sale securities at March 31, 2015 (amounts in thousands):



	Available-for-sale Securities
	Adjusted Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Government agency bonds	$	741,780	$	676	$	(200	)	$	742,256
Municipal bonds	41,552		155		(9		)	41,698
Auction rate securities	9,825		—		—			9,825
Time deposits ⁽¹⁾	506		—		—			506
Corporate bonds and debt	924,818		2,376		(265		)	926,929
Marketable equity securities	1,362		11,804		—			13,166
	$	1,719,843	$	15,011	$	(474	)	$	1,734,380

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

At September 30, 2015, the Company's available-for-sale securities are presented on the condensed consolidated balance sheets as short-term investments of $1,462.5 million and long-term investments of $584.9 million. At March 31, 2015, the Company's available-for-sale securities are presented on the condensed consolidated balance sheets as short-term investments of $1,351.1 million and long-term investments of $383.3 million.

At March 31, 2015, the Company's marketable equity securities consisted of an investment in Hua Hong Semiconductor Limited (Hua Hong), which effected its initial public offering on the Hong Kong stock exchange on October 15, 2014. The Company sold all of its remaining shares of Hua Hong in the three months ended June 30, 2015.

The Company sold available-for-sale securities for proceeds of $46.7 million and $135.8 million during the three and six months ended September 30, 2015, respectively. The Company sold available-for-sale securities for proceeds of $26.7 million and $170.7 million during the three and six months ended September 30, 2014, respectively. The Company had no material realized gains from the sale of available-for-sale securities during the three months ended September 30, 2015. During the six months ended September 30, 2015, the Company had net realized gains of $14.0 million, from sales of available-for-sale marketable equity and debt securities. The Company had no material realized gains from the sale of available-for-sale securities during the three and six months ended September 30, 2014. The Company determines the cost of an investment sold on an average cost basis at the individual security level for sales from multiple lots. For all other sales, the Company uses an adjusted cost basis at the individual security level.

The following tables show all investments in an unrealized loss position for which an other-than-temporary impairment has not been recognized and the related gross unrealized losses and fair value, aggregated by investment category and the length of time that the individual securities have been in a continuous unrealized loss position (amounts in thousands):



	September 30, 2015
	Less than 12 Months					12 Months or Greater					Total
	Fair Value		Unrealized Loss			Fair Value		Unrealized Loss			Fair Value		Unrealized Loss
Government agency bonds	$	140,775	$	(51	)	$	10,000	$	—		$	150,775	$	(51	)
Municipal bonds	34,222		(516		)	—		—			34,222		(516		)
Corporate bonds and debt	391,344		(1,361		)	26,828		(69		)	418,172		(1,430		)
	$	566,341	$	(1,928	)	$	36,828	$	(69	)	$	603,169	$	(1,997	)



	March 31, 2015
	Less than 12 Months					12 Months or Greater					Total
	Fair Value		Unrealized Loss			Fair Value		Unrealized Loss			Fair Value		Unrealized Loss
Government agency bonds	$	162,948	$	(142	)	$	29,942	$	(58	)	$	192,890	$	(200	)
Municipal bonds	13,318		(9		)	—		—			13,318		(9		)
Corporate bonds and debt	163,095		(219		)	19,021		(46		)	182,116		(265		)
	$	339,361	$	(370	)	$	48,963	$	(104	)	$	388,324	$	(474	)

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, 2015 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, 2016, such recovery is not anticipated to occur in the next year and these investments have been classified as long-term investments on the condensed consolidated balance sheet.

The amortized cost and estimated fair value of the available-for-sale securities at September 30, 2015, 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	$	377,682	$	650	$	(42	)	$	378,290
Due after one year and through five years	1,520,303		1,942		(1,954		)	1,520,291
Due after five years and through ten years	132,735		46		(1		)	132,780
Due after ten years	9,825		—		—			9,825
	$	2,040,545	$	2,638	$	(1,997	)	$	2,041,186