Financial Instruments Level within the Fair Value Hierarchy (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Mar. 31, 2013
Assets:
Short-term investments	$ 628,725
Fixed maturities - available for sale	1,057,763
Preferred stock	18,449
Common stock	38,128
Derivatives	1,970
Total	1,745,035
Liabilities:
Guaranteed residual values of TRAC leases	0
Derivatives	39,875	51,550
Total	39,875
Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Short-term investments	628,725
Fixed maturities - available for sale	961,045
Preferred stock	18,449
Common stock	38,128
Derivatives	0
Total	1,646,347
Liabilities:
Guaranteed residual values of TRAC leases	0
Derivatives	0
Total	0
Significant Other Observable Inputs (Level 2)
Assets:
Short-term investments	0
Fixed maturities - available for sale	95,573
Preferred stock	0
Common stock	0
Derivatives	1,970
Total	97,543
Liabilities:
Guaranteed residual values of TRAC leases	0
Derivatives	39,875
Total	39,875
Significant Unobservable Inputs (Level 3)
Assets:
Short-term investments	0
Fixed maturities - available for sale	1,145
Preferred stock	0
Common stock	0
Derivatives	0
Total	1,145
Liabilities:
Guaranteed residual values of TRAC leases	0
Derivatives	0
Total	$ 0