Fair Value Measurements (Financial Instruments Level within the Fair Value Hierarchy) (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Mar. 31, 2021
Assets:
Short-term investments	$ 2,482,154	$ 839,250
Fixed maturities - available for sale	2,821,092	2,653,539
Preferred stock	26,095	21,677
Common stock	46,212	20,440
Derivatives	7,474	6,601
Total	5,383,027	3,541,507
Liabilities:
Derivatives	587	5,141
Total	587	5,141
Level 1 [Member]
Assets:
Short-term investments	2,482,154	839,250
Fixed maturities - available for sale	26,914	6,967
Preferred stock	26,095	21,677
Common stock	46,212	20,440
Derivatives	7,474	6,601
Total	2,588,849	894,935
Liabilities:
Derivatives	0	0
Total	0	0
Level 2 [Member]
Assets:
Short-term investments	0	0
Fixed maturities - available for sale	2,794,086	2,646,415
Preferred stock	0	0
Common stock	0	0
Derivatives	0	0
Total	2,794,086	2,646,415
Liabilities:
Derivatives	587	5,141
Total	587	5,141
Level 3 [Member]
Assets:
Short-term investments	0	0
Fixed maturities - available for sale	92	157
Preferred stock	0	0
Common stock	0	0
Derivatives	0	0
Total	92	157
Liabilities:
Derivatives	0	0
Total	$ 0	$ 0