Accounting Pronouncements (Effects of Adoption of ASU 2018-12 Balance Sheet) (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Mar. 31, 2023	Sep. 30, 2022
Statements Adjusted [Abstract]
Deferred policy acquisition costs, net	$ 121,365	$ 128,463
Assets	19,021,450	18,100,734	$ 18,143,343
Policy benefits and losses, claims and loss expenses payable	865,397	880,202
Deferred income taxes, net	1,444,120	1,329,489
Total liabilities	11,991,072	11,596,543
Accumulated other comprehensive loss	(275,664)	(285,623)
Retained earnings	7,519,376	7,003,148
Stockholders' Equity Attributable to Parent	7,030,378	6,504,191
Liabilities and Equity	19,021,450	18,100,734
Operating Segments [Member] | Life Insurance [Member]
Statements Adjusted [Abstract]
Deferred policy acquisition costs, net	121,365	128,463
Assets	2,881,626	2,891,574
Policy benefits and losses, claims and loss expenses payable	390,607	391,968
Deferred income taxes, net	(74,585)	(77,615)
Total liabilities	2,736,602	2,759,328
Accumulated other comprehensive loss	(218,470)	(225,904)
Retained earnings	334,723	329,379
Stockholders' Equity Attributable to Parent	145,024	132,246
Liabilities and Equity	2,881,626	2,891,574
Previously Reported
Statements Adjusted [Abstract]
Deferred policy acquisition costs, net		152,377
Assets	18,124,648	18,124,648	17,299,581
Policy benefits and losses, claims and loss expenses payable		875,034
Deferred income taxes, net		1,334,427
Total liabilities	$ 11,596,313	11,596,313	$ 11,347,089
Accumulated other comprehensive loss		(267,046)
Retained earnings		7,008,715
Stockholders' Equity Attributable to Parent		6,528,335
Liabilities and Equity		18,124,648
Effect of adoption
Statements Adjusted [Abstract]
Deferred policy acquisition costs, net		(23,914)
Assets		(23,914)
Policy benefits and losses, claims and loss expenses payable		5,168
Deferred income taxes, net		(4,938)
Total liabilities		230
Accumulated other comprehensive loss		(18,577)
Retained earnings		(5,567)
Stockholders' Equity Attributable to Parent		(24,144)
Liabilities and Equity		$ (23,914)