Investments (Table Text Block)	12 Months Ended
	Mar. 31, 2021
Investments, Debt and 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   Allowance for Expected Credit Losses   Fair Value           (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)   (641)   (1,319)   2,043,831 Mortgage-backed securities   174,728   11,706   (1)   (8)   -   186,425   $ 2,405,612 $ 250,254 $ (224) $ (784) $ (1,319) $ 2,653,539   Available-for-sale investments as of March 31, 2020 were as follows:       Amortized Cost   Gross Unrealized Gains   Gross Unrealized Losses More than 12 Months   Gross Unrealized Losses Less than 12 Months   Fair Value           (in thousands) U.S. treasury securities and government obligations $ 112,421 $ 7,959 $ (1) $ - $ 120,379 U.S. government agency mortgage-backed securities   88,449   759   (1)   (373)   88,834 Obligations of states and political subdivisions   287,643   20,664   (155)   -   308,152 Corporate securities   1,656,425   100,302   (919)   (812)   1,754,996 Mortgage-backed securities   187,784   6,011   (1)   (107)   193,687 Redeemable preferred stocks   1,493   72   -   -   1,565   $ 2,334,215 $ 135,767 $ (1,077) $ (1,292) $ 2,467,613
Adjusted Cost and Estimated Market Value of Available-for-sale Investments	March 31, 2021   March 31, 2020     Amortized Cost   Fair Value   Amortized Cost   Fair Value     (In thousands) Due in one year or less $ 90,142 $ 91,190 $ 128,747 $ 129,420 Due after one year through five years   562,442   601,818   547,821   566,934 Due after five years through ten years   672,733   754,536   636,036   678,636 Due after ten years   905,567   1,019,570   832,334   897,371     2,230,884   2,467,114   2,144,938   2,272,361                   Mortgage backed securities   174,728   186,425   187,784   193,687 Redeemable preferred stocks   -   -   1,493   1,565   $ 2,405,612 $ 2,653,539 $ 2,334,215 $ 2,467,613
Available for sale equity investments	March 31, 2021   March 31, 2020     Amortized Cost   Fair Value   Amortized Cost   Fair Value     (In thousands) Common stocks $ 9,775 $ 20,440 $ 9,775 $ 20,015 Non-redeemable preferred stocks   20,034   21,677   5,076   5,110   $ 29,809 $ 42,117 $ 14,851 $ 25,125
Carrying Value of Other Investments	March 31,     2021   2020     (In thousands) Mortgage loans, net $ 391,230 $ 262,688 Short-term investments   7,234   6,995 Real estate   68,813   69,569 Policy loans   11,163   11,212 Other equity investments   11,319   9,909   $ 489,759 $ 360,373