Financial Instruments Level within the Fair Value Hierarchy (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Mar. 31, 2013
Assets:
Short-term investments	$ 516,150
Fixed maturities - available for sale	1,053,578
Preferred stock	22,000
Common stock	41,430
Derivatives	1,212
Total	1,634,370
Liabilities:
Guaranteed residual values of TRAC leases	0
Derivatives	41,749	51,550
Total	41,749
Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Short-term investments	516,150
Fixed maturities - available for sale	938,666
Preferred stock	22,000
Common stock	41,430
Derivatives	0
Total	1,518,246
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	113,737
Preferred stock	0
Common stock	0
Derivatives	1,212
Total	114,949
Liabilities:
Guaranteed residual values of TRAC leases	0
Derivatives	41,749
Total	41,749
Significant Unobservable Inputs (Level 3)
Assets:
Short-term investments	0
Fixed maturities - available for sale	1,175
Preferred stock	0
Common stock	0
Derivatives	0
Total	1,175
Liabilities:
Guaranteed residual values of TRAC leases	0
Derivatives	0
Total	$ 0