Financial Instruments Level within the Fair Value Hierarchy (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Mar. 31, 2013
Assets:
Short-term investments	$ 579,165
Fixed maturities - available for sale	1,083,678
Preferred stock	17,695
Common stock	20,748
Derivatives	2,680
Total	1,703,966
Liabilities:
Guaranteed residual values of TRAC leases	0
Derivatives	35,462	51,550
Total	35,462
Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Short-term investments	579,165
Fixed maturities - available for sale	984,074
Preferred stock	17,695
Common stock	20,748
Derivatives	0
Total	1,601,682
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	98,497
Preferred stock	0
Common stock	0
Derivatives	2,680
Total	101,177
Liabilities:
Guaranteed residual values of TRAC leases	0
Derivatives	35,462
Total	35,462
Significant Unobservable Inputs (Level 3)
Assets:
Short-term investments	0
Fixed maturities - available for sale	1,107
Preferred stock	0
Common stock	0
Derivatives	0
Total	1,107
Liabilities:
Guaranteed residual values of TRAC leases	0
Derivatives	0
Total	$ 0