Accounting Pronouncements (Effects of Adoption of ASU 2018-12 Balance Sheet) (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Mar. 31, 2023	Dec. 31, 2022	Mar. 31, 2022
Statements Adjusted [Abstract]
Deferred policy acquisition costs, net	$ 120,834	$ 128,463
Assets	19,002,576	18,100,734	$ 18,090,124
Policy benefits and losses, claims and loss expenses payable	838,945	880,202
Deferred Income Tax Liabilities, Net	1,427,769	1,329,489
Total liabilities	11,914,775	11,596,543
Accumulated other comprehensive loss	(308,642)	(285,623)
Retained earnings	7,609,777	7,003,148
Stockholders' Equity Attributable to Parent	7,087,801	6,504,191
Liabilities and Equity	19,002,576	18,100,734
Operating Segments [Member] | Life Insurance [Member]
Statements Adjusted [Abstract]
Assets	$ 2,806,247	2,891,574
Previously Reported
Statements Adjusted [Abstract]
Deferred policy acquisition costs, net		152,377
Assets		18,124,648		$ 17,299,581
Policy benefits and losses, claims and loss expenses payable		875,034
Deferred Income Tax Liabilities, Net		1,334,427
Total liabilities		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 Tax Liabilities, 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)