Financial Instruments Level within the Fair Value Hierarchy (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Mar. 31, 2014
Assets:
Short-term investments	$ 503,625us-gaap_TradingSecurities	$ 457,723us-gaap_TradingSecurities
Fixed maturities - available for sale	1,255,104us-gaap_AvailableForSaleSecurities	1,099,467us-gaap_AvailableForSaleSecurities
Preferred stock	16,525uhal_PreferredStockFairValueDisclosure	17,533uhal_PreferredStockFairValueDisclosure
Common stock	22,939uhal_CommonStockFairValueDisclosure	21,275uhal_CommonStockFairValueDisclosure
Derivatives	3,555	3,868
Total	1,801,748us-gaap_AssetsFairValueDisclosure	1,599,866us-gaap_AssetsFairValueDisclosure
Liabilities:
Guaranteed residual values of TRAC leases	0us-gaap_GuaranteesFairValueDisclosure	0us-gaap_GuaranteesFairValueDisclosure
Derivatives	25,271	32,716
Total	25,271us-gaap_LiabilitiesFairValueDisclosure	32,716us-gaap_LiabilitiesFairValueDisclosure
Level 1 [Member]
Assets:
Short-term investments	503,625	457,723
Fixed maturities - available for sale	989,922	898,209
Preferred stock	16,525	17,533
Common stock	22,939	21,275
Derivatives	3,555	3,868
Total	1,536,566	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	264,144	200,154
Preferred stock	0	0
Common stock	0	0
Derivatives	0	0
Total	264,144	200,154
Liabilities:
Guaranteed residual values of TRAC leases	0	0
Derivatives	25,271	32,716
Total	25,271	32,716
Level 3 [Member]
Assets:
Short-term investments	0	0
Fixed maturities - available for sale	1,038	1,104
Preferred stock	0	0
Common stock	0	0
Derivatives	0	0
Total	1,038	1,104
Liabilities:
Guaranteed residual values of TRAC leases	0	0
Derivatives	0	0
Total	$ 0	$ 0

Fair value of common stock at quoted prices in active markets.

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Fair value of preferred stock at quoted prices in active markets.

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Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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Fair value portion of guarantee, including, but not limited to, financial standby letter of credit, fair value guarantee, guarantee of collection of scheduled contractual cash flows from financial assets, and contracts that contingently require the guarantor to make payments or perform services.

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Fair value as of the balance sheet date of interest rate derivative assets, which includes all such derivative instruments in hedging and nonhedging relationships that are recognized as assets.

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Fair value as of the balance sheet date of all derivative liabilities designated as interest rate fair value hedging instruments.

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Fair value of financial and nonfinancial obligations.

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Amount of investments in debt and equity securities and other forms of securities that provide ownership interests classified as trading.

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