Fair Value Measurements (Financial Instruments Level within the Fair Value Hierarchy) (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Mar. 31, 2020
Assets:
Short-term investments	$ 839,250	$ 369,279
Fixed maturities - available for sale	2,653,539	2,466,048
Preferred stock	21,677	6,675
Common stock	20,440	20,015
Derivatives	6,601	5,944
Total	3,541,507	2,867,961
Liabilities:
Derivatives	5,141	8,214
Total	5,141	8,214
Level 1 [Member]
Assets:
Short-term investments	839,250	368,968
Fixed maturities - available for sale	6,967	7,156
Preferred stock	21,677	6,675
Common stock	20,440	20,015
Derivatives	6,601	5,944
Total	894,935	408,758
Liabilities:
Derivatives	0	0
Total	0	0
Level 2 [Member]
Assets:
Short-term investments	0	311
Fixed maturities - available for sale	2,646,415	2,458,731
Preferred stock	0	0
Common stock	0	0
Derivatives	0	0
Total	2,646,415	2,459,042
Liabilities:
Derivatives	5,141	8,214
Total	5,141	8,214
Level 3 [Member]
Assets:
Short-term investments	0	0
Fixed maturities - available for sale	157	161
Preferred stock	0	0
Common stock	0	0
Derivatives	0	0
Total	157	161
Liabilities:
Derivatives	0	0
Total	$ 0	$ 0