Expected maturities may differ from contractual maturities as borrowers may have the right to call or prepay obligations with or without call or prepayment penalties.

We deposit bonds with insurance regulatory authorities to meet statutory requirements. The adjusted cost of bonds on deposit with insurance regulatory authorities was $31.0 million and $30.2 million as of December 31, 2018 and March 31, 2018, respectively.

Available-for-Sale Investments

Available-for-sale investments as of December 31, 2018 were as follows:

		Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses More than 12 Months		Gross Unrealized Losses Less than 12 Months		Estimated Market Value
		(Unaudited)
		(In thousands)
U.S. treasury securities and government obligations	$	128,934	$	1,140	$	(2,319)	$	(2,462)	$	125,293
U.S. government agency mortgage-backed securities		61,243		526		(44)		(1,558)		60,167
Obligations of states and political subdivisions		238,243		5,203		(251)		(2,456)		240,739
Corporate securities		1,576,170		14,898		(8,033)		(26,956)		1,556,079
Mortgage-backed securities		119,006		541		(212)		(1,384)		117,951
Redeemable preferred stocks		1,493		37		–		(20)		1,510
	$	2,125,089	$	22,345	$	(10,859)	$	(34,836)	$	2,101,739

Available-for-sale investments as of March 31, 2018 were as follows:

		Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses More than 12 Months		Gross Unrealized Losses Less than 12 Months		Estimated Market Value

		(In thousands)
U.S. treasury securities and government obligations	$	123,557	$	3,595	$	(1,036)	$	(203)	$	125,913
U.S. government agency mortgage-backed securities		36,416		951		(1)		(93)		37,273
Obligations of states and political subdivisions		178,702		9,938		(217)		(18)		188,405
Corporate securities		1,388,300		50,056		(3,009)		(1,826)		1,433,521
Mortgage-backed securities		94,106		2,072		–		(153)		96,025
Preferred stocks		10,609		321		(29)		(40)		10,861
Common stocks		15,732		12,329		(10)		(189)		27,862
	$	1,847,422	$	79,262	$	(4,302)	$	(2,522)	$	1,919,860

The available-for-sale tables include gross unrealized losses that are not deemed to be other-than-temporarily impaired, aggregated by investment category and length of time that individual securities have been in a continuous unrealized loss position.

We sold available-for-sale securities with a fair value of $76.0 million during the first nine months of fiscal 2019. The gross realized gains on these sales totaled $0.9 million. The gross realized losses on these sales totaled $0.1 million.

The unrealized losses of more than twelve months in the available-for-sale tables are considered temporary declines. We track each investment with an unrealized loss and evaluate it on an individual basis for other-than-temporary impairments including obtaining corroborating opinions from third party sources, performing trend analysis and reviewing management’s future plans. Certain of these investments may have declines determined by management to be other-than-temporary and we recognize these write-downs, if any, through earnings. There were no write downs for the first nine months of fiscal 2019 or 2018.

The investment portfolio primarily consists of corporate securities and obligations of states and political subdivisions. We believe we monitor our investments as appropriate. Our methodology of assessing other-than-temporary impairments is based on security-specific analysis as of the balance sheet date and considers various factors including the length of time to maturity, the extent to which the fair value has been less than the cost, the financial condition and the near-term prospects of the issuer, and whether the debtor is current on its contractually obligated interest and principal payments. Nothing has come to management’s attention that would lead to the belief that any issuer would not have the ability to meet the remaining contractual obligations of the security, including payment at maturity. We have the ability and intent not to sell our fixed maturity and common stock investments for a period of time sufficient to allow us to recover our costs.

The portion of other-than-temporary impairment related to a credit loss is recognized in earnings. The significant inputs utilized in the evaluation of mortgage-backed securities credit losses include ratings, delinquency rates, and prepayment activity. The significant inputs utilized in the evaluation of asset backed securities credit losses include the time frame for principal recovery and the subordination and value of the underlying collateral.

There were no credit losses recognized in earnings for which a portion of an other-than-temporary impairment was recognized in accumulated other comprehensive income (loss) (“AOCI”) for first nine months of fiscal 2019 and fiscal 2018.

The adjusted cost and estimated market value of available-for-sale investments by contractual maturity were as follows:

		December 31, 2018				March 31, 2018
		Amortized Cost		Estimated Market Value		Amortized Cost		Estimated Market Value
		(Unaudited)
		(In thousands)
Due in one year or less	$	58,311	$	58,532	$	36,446	$	36,674
Due after one year through five years		503,227		502,343		441,223		450,816
Due after five years through ten years		648,241		639,629		607,895		626,174
Due after ten years		794,811		781,774		641,411		671,448
		2,004,590		1,982,278		1,726,975		1,785,112

Mortgage-backed securities		119,006		117,951		94,106		96,025
Redeemable preferred stocks		1,493		1,510		2,118		2,247
Equity securities		–		–		24,223		36,476
	$	2,125,089	$	2,101,739	$	1,847,422	$	1,919,860

As of March 31, 2018, equity investments were classified as available-for-sale on our balance sheet. However, upon adoption of Accounting Standards Update (“ASU”) 2016-01, Recognition and Measurement of Financial Assets and Financial Liabilities, on April 1, 2018, the updated guidance eliminated the available-for-sale balance sheet classification for equity investments. As of December 31, 2018 our common stock and non-redeemable preferred stock that are included in Investments, fixed maturities and marketable equities on our balance sheet are stated in the table below. The changes in the fair value of these equity investments are recognized through Net investment and interest income.

Equity investments of common stock and non-redeemable preferred stock were as follows:

		Estimated Market Value as of
		December 31, 2018
		(Unaudited)
		(In thousands)

Common stocks	$	18,298
Non-redeemable preferred stocks		7,305
	$	25,603