Investments (Table Text Block)	3 Months Ended
	Jun. 30, 2022	Jun. 30, 2021
Investments Debt Equity Securities [Abstract]
Available-for-Sale Investments	Amortized   Gross   Gross   Gross   Allowance for Expected Credit Losses   Estimated     (Unaudited)     (In thousands) U.S. treasury securities and government obligations $ 127,940 $   2,947 $   (1,578) $   (2,493) $   – $   126,816 U.S. government agency mortgage-backed securities   37,806   149   (380)   (4,126)   –   33,449 Obligations of states and political subdivisions   166,572   5,830   (1,275)   (2,009)   –   169,118 Corporate securities   1,970,857   38,302   (11,259)   (51,863)   (77)   1,945,960 Mortgage-backed securities   337,023   2,206   (1)   (16,372)   –   322,856  $ 2,640,198 $  49,434 $ ( 14,493 )$ ( 76,863 )$ ( 77 )$  2,598,199	Amortized   Gross   Gross   Gross   Allowance for Expected Credit Losses   Estimated           (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
Adjusted Cost and Estimated Market Value of Available-for-sale Investments	June 30, 2022   March 31, 2022     Amortized   Estimated   Amortized   Estimated     (Unaudited)         (In thousands) Due in one year or less $ 104,389 $ 105,325 $ 97,969 $ 99,432 Due after one year through five years   554,348   557,915   541,840   570,135 Due after five years through ten years   713,435   717,393   704,295   765,073 Due after ten years   931,003   894,710   995,904   1,056,295     2,303,175   2,275,343   2,340,008   2,490,935                   Mortgage-backed securities   337,023   322,856   324,029   330,157  $ 2,640,198 $ 2,598,199 $ 2,664,037 $ 2,821,092
Available for sale equity investments	June 30, 2022   March 31, 2022     Amortized   Estimated   Amortized   Estimated     (Unaudited)             (In thousands)                   Common stocks $ 28,707 $ 45,837 $ 27,674 $ 46,212 Non-redeemable preferred stocks   26,054   25,950   26,054   26,095  $ 54,761 $ 71,787 $ 53,728 $ 72,307
Other investments, carrying value	June 30,   March 31,     2022   2022     (Unaudited)         (In thousands)           Mortgage loans, net $ 433,385 $ 423,163 Short-term investments   34,809   30,916 Real estate   67,539   67,824 Policy loans   10,360   10,309 Other equity investments   11,031   11,543  $ 557,124 $ 543,755