Investments (Table Text Block)	12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
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   Estimated Market 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	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   –   (45)   1,468   $ 2,228,961 $ 26,598 $ (17,025) $ (27,305) $ 2,211,229
Adjusted Cost and Estimated Market Value of Available-for-sale Investments	March 31, 2020   March 31, 2019     Amortized Cost   Estimated Market Value   Amortized Cost   Estimated Market Value     (In thousands) Due in one year or less $ 128,747 $ 129,420 $ 71,987 $ 71,954 Due after one year through five years   547,821   566,934   541,195   540,658 Due after five years through ten years   636,036   678,636   621,031   614,485 Due after ten years   832,334   897,371   845,052   834,769     2,144,938   2,272,361   2,079,265   2,061,866                   Mortgage backed securities   187,784   193,687   148,203   147,895 Redeemable preferred stocks   1,493   1,565   1,493   1,468   $ 2,334,215 $ 2,467,613 $ 2,228,961 $ 2,211,229
Available for sale equity investments	March 31, 2020   March 31, 2019     Amortized Cost   Estimated Market Value   Amortized Cost   Estimated Market Value     (In thousands) Common stocks $ 9,775 $ 20,015 $ 10,123 $ 17,379 Non-redeemable preferred stocks   5,076   5,110   7,451   6,789   $ 14,851 $ 25,125 $ 17,574 $ 24,168
Carrying Value of Other Investments	March 31,     2020   2019     (In thousands) Mortgage loans, net $ 262,688 $ 225,829 Short-term investments   6,995   5,546 Real estate   69,569   53,519 Policy loans   11,212   10,491 Other equity investments   9,909   5,351   $ 360,373 $ 300,736