Fair Value Measurements (Financial Instruments Level within the Fair Value Hierarchy) (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Mar. 31, 2015
Assets:
Short-term investments	$ 499,491	$ 460,762
Fixed maturities - available for sale	1,466,941	1,262,012
Preferred stock	18,428	18,296
Common stock	25,169	24,654
Derivatives	3,344	4,876
Total	$ 2,013,373	$ 1,770,600
Liabilities:
Guaranteed residual values of TRAC leases
Derivatives	$ 14,845	$ 24,484
Total	14,845	24,484
Level 1 [Member]
Assets:
Short-term investments	499,491	460,762
Fixed maturities - available for sale	96,328	101,201
Preferred stock	18,428	18,296
Common stock	25,169	24,654
Derivatives	3,344	4,876
Total	$ 642,760	$ 609,789
Liabilities:
Guaranteed residual values of TRAC leases
Derivatives
Total
Level 2 [Member]
Assets:
Short-term investments
Fixed maturities - available for sale	$ 1,370,275	$ 1,159,807
Preferred stock
Common stock
Derivatives
Total	$ 1,370,275	$ 1,159,807
Liabilities:
Guaranteed residual values of TRAC leases
Derivatives	$ 14,845	$ 24,484
Total	$ 14,845	$ 24,484
Level 3 [Member]
Assets:
Short-term investments
Fixed maturities - available for sale	$ 338	$ 1,004
Preferred stock
Common stock
Derivatives
Total	$ 338	$ 1,004
Liabilities:
Guaranteed residual values of TRAC leases
Derivatives
Total