Investments (Table Text Block)	12 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Investments, Debt and Equity Securities [Abstract]
Available-for-Sale Investments	Amortized   Gross   Gross   Gross   Allowance for Expected Credit Losses   Fair           (In thousands) U.S. treasury securities and government obligations $ 128,078 $   7,984 $   – $   (969) $   – $   135,093 U.S. government agency mortgage-backed securities   44,678   280   (42)   (3,111)   –   41,805 Obligations of states and political subdivisions   178,040   15,450   –   (508)   –   192,982 Corporate securities   1,989,212   138,909   (402)   (6,604)   (60)   2,121,055 Mortgage-backed securities   324,029   7,671   (1)   (1,542)   –   330,157  $ 2,664,037 $  170,294 $ ( 445 )$ ( 12,734 )$ ( 60 )$  2,821,092	Amortized   Gross   Gross   Gross   Allowance for Expected Credit Losses   Fair           (in thousands) U.S. treasury securities and government obligations $ 92,429 $ 12,941 $ – $ – $ – $ 105,370 U.S. government agency mortgage-backed securities   61,427   911   (1)   (132)   –   62,205 Obligations of states and political subdivisions   230,521   25,249   (59)   (3)   –   255,708 Corporate securities   1,846,507   199,447   (163)   (640)   (1,320)   2,043,831 Mortgage-backed securities   174,728   11,706   (1)   (8)   –   186,425  $ 2,405,612 $ 250,254 $( 224 )$( 783 )$( 1,320 )$ 2,653,539
Adjusted Cost and Estimated Market Value of Available-for-sale Investments	March 31, 2022   March 31, 2021     Amortized   Fair   Amortized   Fair     (In thousands) Due in one year or less $ 97,969 $ 99,432 $ 90,142 $ 91,190 Due after one year through five years   541,840   570,135   562,442   601,818 Due after five years through ten years   704,295   765,073   672,733   754,536 Due after ten years   995,904   1,056,295   905,567   1,019,570     2,340,008   2,490,935   2,230,884   2,467,114                   Mortgage backed securities   324,029   330,157   174,728   186,425  $ 2,664,037 $ 2,821,092 $ 2,405,612 $ 2,653,539
Available for sale equity investments	March 31, 2022   March 31, 2021     Amortized   Fair   Amortized   Fair     (In thousands) Common stocks $ 27,674 $ 46,212 $ 9,775 $ 20,440 Non-redeemable preferred stocks   26,054   26,095   20,034   21,677  $ 53,728 $ 72,307 $ 29,809 $ 42,117
Carrying Value of Other Investments	March 31,     2022   2021     (In thousands) Mortgage loans, net $ 423,163 $ 391,230 Short-term investments   30,916   7,234 Real estate   67,824   68,813 Policy loans   10,309   11,163 Other equity investments   11,543   11,319  $ 543,755 $ 489,759