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 $31.1 million and $32.4 million as of September 30, 2018 and March 31, 2018, respectively.

Available-for-Sale Investments

Available-for-sale investments as of September 30, 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	$	125,462	$	1,394	$	(1,688)	$	(1,541)	$	123,627
U.S. government agency mortgage-backed securities		62,273		628		(2)		(981)		61,918
Obligations of states and political subdivisions		204,297		6,623		(229)		(495)		210,196
Corporate securities		1,497,362		17,605		(5,695)		(27,178)		1,482,094
Mortgage-backed securities		101,647		709		–		(1,027)		101,329
Redeemable preferred stocks		1,493		63		–		–		1,556
	$	1,992,534	$	27,022	$	(7,614)	$	(31,222)	$	1,980,720

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
Redeemable preferred stocks		2,118		129		–		–		2,247
	$	1,823,199	$	66,741	$	(4,263)	$	(2,293)	$	1,883,384

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, the updated guidance eliminated the available-for-sale balance sheet classification for equity investments. As of September 30, 2018 and March 31, 2018 we had $8.0 million and $8.6 million of preferred stock and $26.7 million and $27.9 million of common stock, respectively that are included in Investments, fixed maturities and marketable equities on our balance sheet. The changes in the fair value of the equity investments are recognized through Net investment and interest income.

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 $58.3 million during the first six 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 them 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 in the second quarter or for the first six 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 the second quarter or first six months of fiscal 2019 and fiscal 2018, respectively.

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

		September 30, 2018				March 31, 2018
		Amortized Cost		Estimated Market Value		Amortized Cost		Estimated Market Value
		(Unaudited)
		(In thousands)
Due in one year or less	$	54,102	$	54,349	$	36,446	$	36,674
Due after one year through five years		489,499		489,545		441,223		450,816
Due after five years through ten years		625,687		619,371		607,895		626,174
Due after ten years		720,106		714,570		641,411		671,448
		1,889,394		1,877,835		1,726,975		1,785,112

Mortgage backed securities		101,647		101,329		94,106		96,025
Redeemable preferred stocks		1,493		1,556		2,118		2,247
	$	1,992,534	$	1,980,720	$	1,823,199	$	1,883,384