Financial Instruments Level within the Fair Value Hierarchy (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Mar. 31, 2014
Assets:
Short-term investments	$ 639,029	$ 457,723
Fixed maturities - available for sale	1,173,590	1,099,467
Preferred stock	17,204	17,533
Common stock	22,518	21,275
Derivatives	2,712	3,868
Total	1,855,053	1,599,866
Liabilities:
Guaranteed residual values of TRAC leases
Derivatives	31,365	32,716
Total	31,365	32,716
Level 1 [Member]
Assets:
Short-term investments	639,029	457,723
Fixed maturities - available for sale	958,980	898,209
Preferred stock	17,204	17,533
Common stock	22,518	21,275
Derivatives	2,712	3,868
Total	1,640,443	1,398,608
Liabilities:
Guaranteed residual values of TRAC leases
Derivatives
Total
Level 2 [Member]
Assets:
Short-term investments
Fixed maturities - available for sale	213,612	200,154
Preferred stock
Common stock
Derivatives
Total	213,612	200,154
Liabilities:
Guaranteed residual values of TRAC leases
Derivatives	31,365	32,716
Total	31,365	32,716
Level 3 [Member]
Assets:
Short-term investments
Fixed maturities - available for sale	998	1,104
Preferred stock
Common stock
Derivatives
Total	998	1,104
Liabilities:
Guaranteed residual values of TRAC leases
Derivatives
Total