Fair Value Measurements (Financial instruments level within the fair value hierarchy) (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Mar. 31, 2015
Assets:
Short-term investments	$ 557,879	$ 460,762
Fixed maturities - available for sale	1,421,727	1,262,012
Preferred stock	18,170	18,296
Common stock	24,100	24,654
Derivatives	1,906	4,876
Total	$ 2,023,782	$ 1,770,600
Liabilities:
Guaranteed residual values of TRAC leases
Derivatives	$ 15,596	$ 24,484
Total	15,596	24,484
Level 1 [Member]
Assets:
Short-term investments	557,879	460,762
Fixed maturities - available for sale	1,132,444	967,986
Preferred stock	18,170	18,296
Common stock	24,100	24,654
Derivatives	1,906	4,876
Total	$ 1,734,499	$ 1,476,574
Liabilities:
Guaranteed residual values of TRAC leases
Derivatives
Total
Level 2 [Member]
Assets:
Short-term investments
Fixed maturities - available for sale	$ 288,942	$ 293,022
Preferred stock
Common stock
Derivatives
Total	$ 288,942	$ 293,022
Liabilities:
Guaranteed residual values of TRAC leases
Derivatives	$ 15,596	$ 24,484
Total	$ 15,596	$ 24,484
Level 3 [Member]
Assets:
Short-term investments
Fixed maturities - available for sale	$ 341	$ 1,004
Preferred stock
Common stock
Derivatives
Total	$ 341	$ 1,004
Liabilities:
Guaranteed residual values of TRAC leases
Derivatives
Total