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 $17.2 million and $17.3 million at September 30, 2016 and March 31, 2016, respectively.

Available-for-Sale Investments

Available-for-sale investments at September 30, 2016 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	$	73,751	$	7,216	$	–	$	–	$	80,967
U.S. government agency mortgage-backed securities		29,902		2,116		(6)		(2)		32,010
Obligations of states and political subdivisions		161,620		16,285		(11)		–		177,894
Corporate securities		1,198,017		67,183		(7,775)		(3,266)		1,254,159
Mortgage-backed securities		42,765		1,238		–		(38)		43,965
Redeemable preferred stocks		15,332		795		–		(127)		16,000
Common stocks		17,970		9,482		(10)		(17)		27,425
	$	1,539,357	$	104,315	$	(7,802)	$	(3,450)	$	1,632,420

Available-for-sale investments at March 31, 2016 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	$	85,861	$	3,791	$	–	$	(193)	$	89,459
U.S. government agency mortgage-backed securities		21,845		1,596		(6)		(39)		23,396
Obligations of states and political subdivisions		166,725		10,660		(81)		(414)		176,890
Corporate securities		1,143,125		26,861		(8,013)		(28,181)		1,133,792
Mortgage-backed securities		42,991		475		–		(62)		43,404
Redeemable preferred stocks		17,977		556		–		(105)		18,428
Common stocks		17,732		7,822		(10)		(375)		25,169
	$	1,496,256	$	51,761	$	(8,110)	$	(29,369)	$	1,510,538

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 $120.7 million during the first six months of fiscal 2017. The gross realized gains on these sales totaled $3.1 million. The gross realized losses on these sales totaled $0.9 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 in the second quarter or for the first six months of fiscal 2017 or 2016.

The investment portfolio primarily consists of corporate securities and U.S. government securities. 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 each 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 credit losses on mortgage backed securities include ratings, delinquency rates, and prepayment activity. The significant inputs utilized in the evaluation of credit losses on asset backed securities 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) for the second quarter or first six months of fiscal 2017.

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

		September 30, 2016				March 31, 2016
		Amortized Cost		Estimated Market Value		Amortized Cost		Estimated Market Value
		(Unaudited)
		(In thousands)
Due in one year or less	$	29,344	$	29,790	$	48,679	$	49,146
Due after one year through five years		316,614		330,006		250,576		256,597
Due after five years through ten years		570,836		602,486		557,984		557,961
Due after ten years		546,496		582,748		560,317		559,833
		1,463,290		1,545,030		1,417,556		1,423,537

Mortgage backed securities		42,765		43,965		42,991		43,404
Redeemable preferred stocks		15,332		16,000		17,977		18,428
Common stocks		17,970		27,425		17,732		25,169
	$	1,539,357	$	1,632,420	$	1,496,256	$	1,510,538