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 March 31, 2018 (amounts in millions):



	Available-for-sale Securities
	Adjusted Cost		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value
Government agency bonds	$	723.2	$	—	$	—	$	723.2
Municipal bonds - taxable	14.9		—		—		14.9
Time deposits	11.5		—		—		11.5
Corporate bonds and debt	542.9		—		—		542.9
Marketable equity securities	0.7		2.1		—		2.8
Total	$	1,293.2	$	2.1	$	—	$	1,295.3

The following is a summary of available-for-sale securities at March 31, 2017 (amounts in millions):



	Available-for-sale Securities
	Adjusted Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Government agency bonds	$	227.1	$	—	$	(0.2	)	$	226.9
Municipal bonds - tax exempt	55.3		—		—			55.3
Municipal bonds - taxable	10.0		—		—			10.0
Corporate bonds and debt	207.9		0.1		(0.2		)	207.8
Marketable equity securities	0.7		0.9		—			1.6
Total	$	501.0	$	1.0	$	(0.4	)	$	501.6

At March 31, 2018, all of the Company's available-for-sale securities are presented on the consolidated balance sheets as short-term investments of $1,295.3 million. All available-for-sale debt securities are classified as short-term on the consolidated balance sheet because the Company intends to sell them in the first quarter of fiscal 2019 to fund the closing of its pending acquisition of Microsemi. At March 31, 2017, the Company's available-for-sale securities are presented on the consolidated balance sheets as short-term investments of $394.1 million and long-term investments of $107.5 million.

There were no sales of available-for-sale investments during the year ended March 31, 2018. The Company sold available-for-sale investments for proceeds of $470.2 million and $1,501.5 million during the years ended March 31, 2017 and 2016, respectively. The Company had no material net realized gains from sales of available-for-sale marketable equity and debt securities during the years ended March 31, 2018 and March 31, 2017 compared to gains of $13.7 million during the year ended March 31, 2016. During the three months ended March 31, 2018, the Company recognized an impairment of $15.5 million on available-for-sale investments based on its evaluation of available evidence and the Company's intent to sell these investments during the first quarter of fiscal 2019 to fund its pending acquisition of Microsemi. The Company determines the cost of available-for-sale debt securities sold on a first-in first-out (FIFO) basis at the individual security level for sales from multiple lots. For sales of marketable equity securities, the Company uses an average cost basis at the individual security level. Gains and losses recognized in earnings are credited or charged to other income (expense) on the consolidated statements of income.

As of March 31, 2018, the Company did not have any investments in an unrealized position for which an other-than-temporary impairment had not been recognized. The following table 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 during the year ended March 31, 2017 (amounts in millions):



	March 31, 2017
	Less than 12 Months					12 Months or Greater				Total
	Fair Value		Unrealized Loss			Fair Value		Unrealized Loss		Fair Value		Unrealized Loss
Government agency bonds	$	196.9	$	(0.2	)	$	—	$	—	$	196.9	$	(0.2	)
Municipal bonds - tax exempt	55.3		—			—		—		55.3		—
Corporate bonds and debt	132.8		(0.2		)	—		—		132.8		(0.2		)
Total	$	385.0	$	(0.4	)	$	—	$	—	$	385.0	$	(0.4	)

The amortized cost and estimated fair value of the available-for-sale securities at March 31, 2018, by contractual maturity, excluding marketable equity securities of $2.8 million, which have no contractual maturity, are shown below (amounts in millions). 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	$	246.5	$	—	$	—	$	246.5
Due after one year and through five years	1,046.0		—		—		1,046.0
Due after five years and through ten years	—		—		—		—
Due after ten years	—		—		—		—
Total	$	1,292.5	$	—	$	—	$	1,292.5

The amortized cost and estimated fair value of the available-for-sale securities at March 31, 2017, by maturity, excluding marketable equity securities of $1.6 million, which have no contractual maturity, are shown below (amounts in millions).



	Adjusted Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Available-for-sale
Due in one year or less	$	342.7	$	—	$	(0.2	)	$	342.5
Due after one year and through five years	157.6		0.1		(0.2		)	157.5
Due after five years and through ten years	—		—		—			—
Due after ten years	—		—		—			—
Total	$	500.3	$	0.1	$	(0.4	)	$	500.0