Fair Value Measurements (Financial Instruments Level within the Fair Value Hierarchy) (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Mar. 31, 2018
Assets:
Short-term investments	$ 463,847	$ 475,320
Fixed maturities - available for sale	2,209,761	1,881,137
Preferred stock	8,257	10,861
Common stock	17,379	27,862
Derivatives	1,607	4,825
Total	2,700,851	2,400,005
Liabilities:
Derivatives		897
Total		897
Level 1 [Member]
Assets:
Short-term investments	463,599	475,320
Fixed maturities - available for sale	7,327	7,567
Preferred stock	8,257	10,861
Common stock	17,379	27,862
Derivatives	1,468	4,388
Total	498,030	525,998
Liabilities:
Derivatives
Total
Level 2 [Member]
Assets:
Short-term investments	248
Fixed maturities - available for sale	2,202,213	1,873,293
Preferred stock
Common stock
Derivatives	139	437
Total	2,202,600	1,873,730
Liabilities:
Derivatives		897
Total		897
Level 3 [Member]
Assets:
Short-term investments
Fixed maturities - available for sale	221	277
Preferred stock
Common stock
Derivatives
Total	221	277
Liabilities:
Derivatives
Total