v3.25.4
Investments (Available For Sale Investments) (Details) - USD ($)
$ in Thousands
Dec. 31, 2025
Mar. 31, 2025
Available-for-sale Securities [Abstract]    
Debt Securities, Available-for-Sale, Amortized Cost, Current $ 2,649,214 $ 2,708,562
Available For Sale Debt Securities Accumulated Gross Unrealized Gain 11,076 2,915
Gross unrealized losses more than 12 months (155,065) (228,875)
Allowance for expected credit loss (3,789) (3,104)
Available for sale investments, estimated market value 2,501,436 2,479,498
U.S. treasury securities and government obligations [Member]    
Available-for-sale Securities [Abstract]    
Debt Securities, Available-for-Sale, Amortized Cost, Current 104,262 119,289
Available For Sale Debt Securities Accumulated Gross Unrealized Gain 265 206
Gross unrealized losses more than 12 months (5,320) (8,353)
Available for sale investments, estimated market value 99,207 111,142
U.S. government agency mortgage-backed securities [Member]    
Available-for-sale Securities [Abstract]    
Debt Securities, Available-for-Sale, Amortized Cost, Current 156,754 81,909
Available For Sale Debt Securities Accumulated Gross Unrealized Gain 1,024 232
Gross unrealized losses more than 12 months (7,672) (8,712)
Available for sale investments, estimated market value 150,106 73,429
Obligations of states and political subdivisions [Member]    
Available-for-sale Securities [Abstract]    
Debt Securities, Available-for-Sale, Amortized Cost, Current 133,861 137,280
Available For Sale Debt Securities Accumulated Gross Unrealized Gain 520 272
Gross unrealized losses more than 12 months (5,904) (8,808)
Available for sale investments, estimated market value 128,477 128,744
Corporate securities [Member]    
Available-for-sale Securities [Abstract]    
Debt Securities, Available-for-Sale, Amortized Cost, Current 1,660,382 1,807,605
Available For Sale Debt Securities Accumulated Gross Unrealized Gain 5,420 1,623
Gross unrealized losses more than 12 months (102,335) (155,749)
Allowance for expected credit loss (3,789) (3,104)
Available for sale investments, estimated market value 1,559,678 1,650,375
Mortgage-backed securities [Member]    
Available-for-sale Securities [Abstract]    
Debt Securities, Available-for-Sale, Amortized Cost, Current 593,955 562,479
Available For Sale Debt Securities Accumulated Gross Unrealized Gain 3,847 582
Gross unrealized losses more than 12 months (33,834) (47,253)
Available for sale investments, estimated market value $ 563,968 $ 515,808