Accounting Pronouncements (Transition Adjustment Stockholders' Equity) (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Sep. 30, 2023	Mar. 31, 2023	Dec. 31, 2022	Sep. 30, 2022	Mar. 31, 2022
Liability For Future Policy Benefits [Abstract]
Deferred acquisition costs and related asset balances	$ 120,834		$ 128,463	$ 133,720		$ 131,430
Tax effect	308,642		285,623
Stockholders' Equity Attributable to Parent	7,087,801		6,504,191
Accumulated Other Comprehensive Income (Loss) [Member]
Liability For Future Policy Benefits [Abstract]
Tax effect	308,642	$ 275,664	$ 285,623	$ 303,736	$ 243,497	$ 4,992
Cumulative Effect Period Of Adoption Adjustment [Member] | Retained Earnings [Member]
Liability For Future Policy Benefits [Abstract]
Liability For Future Policy Benefits	(4,327)
Market risk benefits	(3,791)
Stockholders' Equity Attributable to Parent	(8,118)
Cumulative Effect Period Of Adoption Adjustment [Member] | Accumulated Other Comprehensive Income (Loss) [Member]
Liability For Future Policy Benefits [Abstract]
Liability For Future Policy Benefits	(123,132)
Deferred acquisition costs and related asset balances	41,438
Tax effect	17,156
Stockholders' Equity Attributable to Parent	$ (64,538)