Financial Instruments Level within the Fair Value Hierarchy (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Mar. 31, 2014
Assets:
Short-term investments	$ 820,060	$ 457,723
Fixed maturities - available for sale	1,219,594	1,099,467
Preferred stock	17,721	17,533
Common stock	22,816	21,275
Derivatives	2,623	3,868
Total	2,082,814	1,599,866
Liabilities:
Guaranteed residual values of TRAC leases	0	0
Derivatives	26,859	32,716
Total	26,859	32,716
Level 1 [Member]
Assets:
Short-term investments	820,060	457,723
Fixed maturities - available for sale	982,453	898,209
Preferred stock	17,721	17,533
Common stock	22,816	21,275
Derivatives	2,623	3,868
Total	1,845,673	1,398,608
Liabilities:
Guaranteed residual values of TRAC leases	0	0
Derivatives	0	0
Total	0	0
Level 2 [Member]
Assets:
Short-term investments	0	0
Fixed maturities - available for sale	236,178	200,154
Preferred stock	0	0
Common stock	0	0
Derivatives	0	0
Total	236,178	200,154
Liabilities:
Guaranteed residual values of TRAC leases	0	0
Derivatives	26,859	32,716
Total	26,859	32,716
Level 3 [Member]
Assets:
Short-term investments	0	0
Fixed maturities - available for sale	963	1,104
Preferred stock	0	0
Common stock	0	0
Derivatives	0	0
Total	963	1,104
Liabilities:
Guaranteed residual values of TRAC leases	0	0
Derivatives	0	0
Total	$ 0	$ 0