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 debt securities at December 31, 2018 (in millions):



	Available-for-sale Debt Securities
	Adjusted Cost		Gross Unrealized Gains	Gross Unrealized Losses	Estimated Fair Value
Time deposits	$	2.3	—	—	$	2.3

At December 31, 2018, short-term investments of $4.0 million included available-for-sale debt securities of $2.3 million and marketable equity securities of $1.7 million.

The following is a summary of available-for-sale debt securities at March 31, 2018 (in millions):



	Available-for-sale Debt Securities
	Adjusted Cost		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value
Available-for-sale debt securities:
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
Total	$	1,292.5	$	—	$	—	$	1,292.5

At March 31, 2018, short-term investments of $1.30 billion included available-for-sale debt securities of $1.29 billion and marketable equity securities of $2.8 million.

The Company sold available-for-sale debt securities for proceeds of $1.38 billion during the nine months ended December 31, 2018 to help finance the acquisition of Microsemi. The Company had no sales of available-for-sale debt securities during the nine months ended December 31, 2017. During the nine months ended December 31, 2018, the Company recognized losses of $5.6 million on available-for-sale debt securities and $1.2 million on marketable equity securities. During fiscal 2018, the Company recognized an impairment of $15.5 million on available-for-sale debt securities based on its evaluation of available evidence and the Company's intent to sell these investments which were subsequently sold in the first quarter of fiscal 2019. 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 condensed consolidated statements of operations.

As of December 31, 2018 and March 31, 2018, the Company had no available-for-sale debt securities in an unrealized loss position.

The amortized cost and estimated fair value of the available-for-sale debt securities at December 31, 2018, by contractual maturity are shown below (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 debt securities as available for current operations.



	Adjusted Cost		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value
Available-for-sale debt securities
Due in one year or less	$	2.3	$	—	$	—	$	2.3