Fair Value Measurements (Financial Instruments Level within the Fair Value Hierarchy) (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Mar. 31, 2019
Assets:
Short-term investments	$ 369,279	$ 463,847
Fixed maturities - available for sale	2,466,048	2,209,761
Preferred stock	6,675	8,257
Common stock	20,015	17,379
Derivatives	5,944	1,607
Total	2,867,961	2,700,851
Liabilities:
Derivatives	8,214	0
Total	8,214	0
Level 1 [Member]
Assets:
Short-term investments	368,968	463,599
Fixed maturities - available for sale	7,156	7,327
Preferred stock	6,675	8,257
Common stock	20,015	17,379
Derivatives	5,944	1,468
Total	408,758	498,030
Liabilities:
Derivatives	0	0
Total	0	0
Level 2 [Member]
Assets:
Short-term investments	311	248
Fixed maturities - available for sale	2,458,731	2,202,213
Preferred stock	0	0
Common stock	0	0
Derivatives	0	139
Total	2,459,042	2,202,600
Liabilities:
Derivatives	8,214	0
Total	8,214	0
Level 3 [Member]
Assets:
Short-term investments	0	0
Fixed maturities - available for sale	161	221
Preferred stock	0	0
Common stock	0	0
Derivatives	0	0
Total	161	221
Liabilities:
Derivatives	0	0
Total	$ 0	$ 0