Fair Value Measurements (Financial Instruments Level within the Fair Value Hierarchy) (Details) - USD ($) $ in Thousands	Mar. 31, 2023	Mar. 31, 2022
Assets:
Short-term investments	$ 1,809,441	$ 2,482,154
Fixed maturities - available for sale	2,709,037	2,821,092
Preferred stock	21,982	26,095
Common stock	39,375	46,212
Derivatives	9,606	7,474
Total	4,589,441	5,383,027
Liabilities:
Derivatives	0	587
Total	0	587
Level 1 [Member]
Assets:
Short-term investments	1,808,797	2,482,154
Fixed maturities - available for sale	251,832	26,914
Preferred stock	21,982	26,095
Common stock	39,375	46,212
Derivatives	4,295	7,474
Total	2,126,281	2,588,849
Liabilities:
Derivatives	0	0
Total	0	0
Level 2 [Member]
Assets:
Short-term investments	644	0
Fixed maturities - available for sale	2,457,146	2,794,086
Preferred stock	0	0
Common stock	0	0
Derivatives	5,311	0
Total	2,463,101	2,794,086
Liabilities:
Derivatives	0	587
Total	0	587
Level 3 [Member]
Assets:
Short-term investments	0	0
Fixed maturities - available for sale	59	92
Preferred stock	0	0
Common stock	0	0
Derivatives	0	0
Total	59	92
Liabilities:
Derivatives	0	0
Total	$ 0	$ 0