Financial Instruments Level within the Fair Value Hierarchy (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Mar. 31, 2012
Assets:
Short-term investments	$ 572,104
Fixed maturities - available for sale	863,059
Preferred stock	24,558
Common stock	16,829
Derivatives	185
Total	1,476,735
Liabilities:
Guaranteed residual values of TRAC leases	0
Derivatives	60,301	59,313
Total	60,301
Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Short-term investments	572,104
Fixed maturities - available for sale	779,318
Preferred stock	24,558
Common stock	16,829
Derivatives	0
Total	1,392,809
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	82,544
Preferred stock	0
Common stock	0
Derivatives	185
Total	82,729
Liabilities:
Guaranteed residual values of TRAC leases	0
Derivatives	60,301
Total	60,301
Significant Unobservable Inputs (Level 3)
Assets:
Short-term investments	0
Fixed maturities - available for sale	1,197
Preferred stock	0
Common stock	0
Derivatives	0
Total	1,197
Liabilities:
Guaranteed residual values of TRAC leases	0
Derivatives	0
Total	$ 0