Financial Instruments Level within the Fair Value Hierarchy (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Mar. 31, 2012
Assets:
Short-term investments	$ 561,798
Fixed maturities - available for sale	972,887
Preferred stock	22,208
Common stock	24,873
Derivatives	984
Total	1,582,750
Liabilities:
Guaranteed residual values of TRAC leases	0
Derivatives	56,089	59,313
Total	56,089
Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Short-term investments	561,798
Fixed maturities - available for sale	894,395
Preferred stock	22,208
Common stock	24,873
Derivatives	0
Total	1,503,274
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	77,298
Preferred stock	0
Common stock	0
Derivatives	984
Total	78,282
Liabilities:
Guaranteed residual values of TRAC leases	0
Derivatives	56,089
Total	56,089
Significant Unobservable Inputs (Level 3)
Assets:
Short-term investments	0
Fixed maturities - available for sale	1,194
Preferred stock	0
Common stock	0
Derivatives	0
Total	1,194
Liabilities:
Guaranteed residual values of TRAC leases	0
Derivatives	0
Total	$ 0