Investments (Table Text Block)

3 Months Ended

6 Months Ended

Mar. 31, 2019

Sep. 30, 2019

Investments Debt Equity Securities [Abstract]

Available-for-Sale Investments

		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	$	136,010	$	2,409	$	(2,104)	$	(447)	$	135,868
U.S. government agency mortgage-backed securities		31,101		433		(146)		(19)		31,369
Obligations of states and political subdivisions		298,955		8,079		(233)		(905)		305,896
Corporate securities		1,613,199		14,777		(14,257)		(24,986)		1,588,733
Mortgage-backed securities		148,203		880		(285)		(903)		147,895
Redeemable preferred stocks		1,493		20		0		(45)		1,468
	$	2,228,961	$	26,598	$	(17,025)	$	(27,305)	$	2,211,229

		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	$	133,938	$	7,673	$	(148)	$	0	$	141,463
U.S. government agency mortgage-backed securities		40,588		694		(2)		0		41,280
Obligations of states and political subdivisions		296,325		20,642		(155)		0		316,812
Corporate securities		1,654,981		77,467		(2,329)		(176)		1,729,943
Mortgage-backed securities		150,143		5,529		(1)		(49)		155,622
Redeemable preferred stocks		1,493		74		0		0		1,567
	$	2,277,468	$	112,079	$	(2,635)	$	(225)	$	2,386,687

Adjusted Cost and Estimated Market Value of Available-for-sale Investments

		September 30, 2019				March 31, 2019
		Amortized Cost		Estimated Market Value		Amortized Cost		Estimated Market Value
		(Unaudited)
		(In thousands)
Due in one year or less	$	83,028	$	83,337	$	71,987	$	71,954
Due after one year through five years		521,038		536,225		541,195		540,658
Due after five years through ten years		694,348		729,026		621,031		614,485
Due after ten years		827,418		880,910		845,052		834,769
		2,125,832		2,229,498		2,079,265		2,061,866
Mortgage-backed securities		150,143		155,622		148,203		147,895
Redeemable preferred stocks		1,493		1,567		1,493		1,468
	$	2,277,468	$	2,386,687	$	2,228,961	$	2,211,229

Available for sale equity investments

		September 30, 2019				March 31, 2019
		Amortized Cost		Estimated Market Value		Amortized Cost		Estimated Market Value
		(Unaudited)
		(In thousands)
Common stocks	$	10,123	$	19,207	$	10,123	$	17,379
Non-redeemable preferred stocks		7,451		7,456		7,451		6,789
	$	17,574	$	26,663	$	17,574	$	24,168