Consolidated Balance Sheet by Industry Segment (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015		Mar. 31, 2014		Mar. 31, 2013		Mar. 31, 2012
ASSETS:
Cash and cash equivalents	$ 441,850		$ 495,112		$ 463,744		$ 357,180
Reinsurance recoverables and trade receivables, net	189,869		199,322
Inventories, net	69,472		67,020
Prepaid expenses	126,296		55,269
Investments, fixed maturities and marketable equities	1,304,962		1,138,275
Investments, other	268,720		248,850
Deferred policy acquisition costs, net	115,422		118,707
Other assets	106,157		97,588
Related party assets	141,790		169,624
Subtotal assets	2,764,538		2,589,767
Investments in subsidiaries
Property, plant and equipment, at cost:
Land	467,482		405,177
Buildings and improvements	1,728,033		1,430,272
Furniture and equipment	355,349		322,146
Property, plant and equipment (gross)	6,047,493		5,141,717
Less: Accumulated depreciation	(1,939,856)		(1,732,506)
Total property, plant and equipment	4,107,637		3,409,211
Total assets	6,872,175		5,998,978		5,306,601
Liabilities:
Accounts payable and accrued expenses	495,135		357,954
Notes, loans and leases payable	2,190,869		1,942,359
Policy benefits and losses, claims and loss expenses payable	1,062,188		1,082,598
Liabilities from investment contracts	685,745		616,725
Other policyholders' funds and liabilities	8,999		7,988
Deferred income	18,081		31,390
Deferred income taxes, net	526,799		432,596
Related party liabilities	0		0
Total liabilities	4,987,816		4,471,610
Stockholders' equity:
Additional paid-in capital	449,668		444,210
Accumulated other comprehensive loss	(34,365)		(53,923)
Retained earnings	2,142,600		1,805,453
Unearned employee stock ownership plan shares	(6,391)		(1,219)
Total stockholders' equity	1,884,359		1,527,368
Total liabilities and stockholders' equity	6,872,175		5,998,978
Rental Trailers and Other Rental Equipment [Member]
Property, plant and equipment, at cost:
Property subject to or available for operating lease, gross	436,642		373,325
Rental Trucks [Member]
Property, plant and equipment, at cost:
Property subject to or available for operating lease, gross	3,059,987		2,610,797
Series A Preferred Stock [Member]
Stockholders' equity:
Preferred stock, value, issued
Series B Preferred Stock [Member]
Stockholders' equity:
Preferred stock, value, issued
Series A Common Stock [Member]
Stockholders' equity:
Common stock, value, issued
Amerco Common Stock [Member]
Stockholders' equity:
Common stock, value, issued	10,497		10,497
Common Stock in Treasury [Member]
Stockholders' equity:
Treasury stock, value	(525,653)		(525,653)
Preferred Stock in Treasury [Member]
Stockholders' equity:
Treasury stock, value	(151,997)		(151,997)
Operating Segments [Member] | Moving and Storage Consolidations [Member]
ASSETS:
Cash and cash equivalents	431,873		464,710		427,560		309,228
Reinsurance recoverables and trade receivables, net	32,364		28,961
Inventories, net	69,472		67,020
Prepaid expenses	126,296		55,269
Investments, fixed maturities and marketable equities	0		0
Investments, other	27,637		32,850
Deferred policy acquisition costs, net	0		0
Other assets	101,689		93,857
Related party assets	144,040		172,507
Subtotal assets	933,371		915,174
Investments in subsidiaries	443,462		373,490
Property, plant and equipment, at cost:
Land	467,482		405,177
Buildings and improvements	1,728,033		1,430,272
Furniture and equipment	355,349		322,146
Property, plant and equipment (gross)	6,047,493		5,141,717
Less: Accumulated depreciation	(1,939,856)		(1,732,506)
Total property, plant and equipment	4,107,637		3,409,211
Total assets	5,484,470		4,697,875
Liabilities:
Accounts payable and accrued expenses	489,140		356,211
Notes, loans and leases payable	2,190,869		1,942,359
Policy benefits and losses, claims and loss expenses payable	363,552		370,668
Liabilities from investment contracts	0		0
Other policyholders' funds and liabilities	0		0
Deferred income	18,081		31,390
Deferred income taxes, net	524,550		455,295
Related party liabilities	13,919		14,584
Total liabilities	3,600,111		3,170,507
Stockholders' equity:
Additional paid-in capital	449,878		444,420
Accumulated other comprehensive loss	(34,365)		(53,923)
Retained earnings	2,142,390		1,805,243
Unearned employee stock ownership plan shares	(6,391)		(1,219)
Total stockholders' equity	1,884,359		1,527,368
Total liabilities and stockholders' equity	5,484,470		4,697,875
Operating Segments [Member] | Moving and Storage Consolidations [Member] | Rental Trailers and Other Rental Equipment [Member]
Property, plant and equipment, at cost:
Property subject to or available for operating lease, gross	436,642		373,325
Operating Segments [Member] | Moving and Storage Consolidations [Member] | Rental Trucks [Member]
Property, plant and equipment, at cost:
Property subject to or available for operating lease, gross	3,059,987		2,610,797
Operating Segments [Member] | Moving and Storage Consolidations [Member] | Series A Preferred Stock [Member]
Stockholders' equity:
Preferred stock, value, issued
Operating Segments [Member] | Moving and Storage Consolidations [Member] | Series B Preferred Stock [Member]
Stockholders' equity:
Preferred stock, value, issued
Operating Segments [Member] | Moving and Storage Consolidations [Member] | Series A Common Stock [Member]
Stockholders' equity:
Common stock, value, issued
Operating Segments [Member] | Moving and Storage Consolidations [Member] | Amerco Common Stock [Member]
Stockholders' equity:
Common stock, value, issued	10,497		10,497
Operating Segments [Member] | Moving and Storage Consolidations [Member] | Common Stock in Treasury [Member]
Stockholders' equity:
Treasury stock, value	(525,653)		(525,653)
Operating Segments [Member] | Moving and Storage Consolidations [Member] | Preferred Stock in Treasury [Member]
Stockholders' equity:
Treasury stock, value	(151,997)		(151,997)
Operating Segments [Member] | Property and Casualty Insurance [Member]
ASSETS:
Cash and cash equivalents	8,495	[1]	12,758	[2]	14,120	[3]	22,542	[4]
Reinsurance recoverables and trade receivables, net	125,506	[1]	142,335	[2]
Inventories, net	0	[1]	0	[2]
Prepaid expenses	0	[1]	0	[2]
Investments, fixed maturities and marketable equities	228,530	[1]	192,173	[2]
Investments, other	50,867	[1]	54,674	[2]
Deferred policy acquisition costs, net	0	[1]	0	[2]
Other assets	1,924	[1]	1,991	[2]
Related party assets	13,268	[1]	13,011	[2]
Subtotal assets	428,590	[1]	416,942	[2]
Investments in subsidiaries	0	[1]	0	[2]
Property, plant and equipment, at cost:
Land	0	[1]	0	[2]
Buildings and improvements	0	[1]	0	[2]
Furniture and equipment	0	[1]	0	[2]
Property, plant and equipment (gross)	0	[1]	0	[2]
Less: Accumulated depreciation	0	[1]	0	[2]
Total property, plant and equipment	0	[1]	0	[2]
Total assets	428,590	[1]	416,942	[2]
Liabilities:
Accounts payable and accrued expenses	0	[1]	0	[2]
Notes, loans and leases payable	0	[1]	0	[2]
Policy benefits and losses, claims and loss expenses payable	271,744	[1]	295,216	[2]
Liabilities from investment contracts	0	[1]	0	[2]
Other policyholders' funds and liabilities	4,072	[1]	3,732	[2]
Deferred income	0	[1]	0	[2]
Deferred income taxes, net	(18,592)	[1]	(30,440)	[2]
Related party liabilities	2,073	[1]	1,647	[2]
Total liabilities	259,297	[1]	270,155	[2]
Stockholders' equity:
Additional paid-in capital	91,120	[1]	91,120	[2]
Accumulated other comprehensive loss	8,871	[1]	1,782	[2]
Retained earnings	66,001	[1]	50,584	[2]
Unearned employee stock ownership plan shares	0	[1]	0	[2]
Total stockholders' equity	169,293	[1]	146,787	[2]
Total liabilities and stockholders' equity	428,590	[1]	416,942	[2]
Operating Segments [Member] | Property and Casualty Insurance [Member] | Rental Trailers and Other Rental Equipment [Member]
Property, plant and equipment, at cost:
Property subject to or available for operating lease, gross	0	[1]	0	[2]
Operating Segments [Member] | Property and Casualty Insurance [Member] | Rental Trucks [Member]
Property, plant and equipment, at cost:
Property subject to or available for operating lease, gross	0	[1]	0	[2]
Operating Segments [Member] | Property and Casualty Insurance [Member] | Series A Preferred Stock [Member]
Stockholders' equity:
Preferred stock, value, issued		[1]		[2]
Operating Segments [Member] | Property and Casualty Insurance [Member] | Series B Preferred Stock [Member]
Stockholders' equity:
Preferred stock, value, issued		[1]		[2]
Operating Segments [Member] | Property and Casualty Insurance [Member] | Series A Common Stock [Member]
Stockholders' equity:
Common stock, value, issued		[1]		[2]
Operating Segments [Member] | Property and Casualty Insurance [Member] | Amerco Common Stock [Member]
Stockholders' equity:
Common stock, value, issued	3,301	[1]	3,301	[2]
Operating Segments [Member] | Property and Casualty Insurance [Member] | Common Stock in Treasury [Member]
Stockholders' equity:
Treasury stock, value	0	[1]	0	[2]
Operating Segments [Member] | Property and Casualty Insurance [Member] | Preferred Stock in Treasury [Member]
Stockholders' equity:
Treasury stock, value	0	[1]	0	[2]
Operating Segments [Member] | Life Insurance [Member]
ASSETS:
Cash and cash equivalents	1,482	[1]	17,644	[2]	22,064	[3]	25,410	[4]
Reinsurance recoverables and trade receivables, net	31,999	[1]	28,026	[2]
Inventories, net	0	[1]	0	[2]
Prepaid expenses	0	[1]	0	[2]
Investments, fixed maturities and marketable equities	1,076,432	[1]	946,102	[2]
Investments, other	190,216	[1]	161,326	[2]
Deferred policy acquisition costs, net	115,422	[1]	118,707	[2]
Other assets	2,544	[1]	1,740	[2]
Related party assets	586	[1]	515	[2]
Subtotal assets	1,418,681	[1]	1,274,060	[2]
Investments in subsidiaries	0	[1]	0	[2]
Property, plant and equipment, at cost:
Land	0	[1]	0	[2]
Buildings and improvements	0	[1]	0	[2]
Furniture and equipment	0	[1]	0	[2]
Property, plant and equipment (gross)	0	[1]	0	[2]
Less: Accumulated depreciation	0	[1]	0	[2]
Total property, plant and equipment	0	[1]	0	[2]
Total assets	1,418,681	[1]	1,274,060	[2]
Liabilities:
Accounts payable and accrued expenses	5,995	[1]	1,743	[2]
Notes, loans and leases payable	0	[1]	0	[2]
Policy benefits and losses, claims and loss expenses payable	426,892	[1]	416,714	[2]
Liabilities from investment contracts	685,745	[1]	616,725	[2]
Other policyholders' funds and liabilities	4,927	[1]	4,256	[2]
Deferred income	0	[1]	0	[2]
Deferred income taxes, net	20,841	[1]	7,741	[2]
Related party liabilities	112	[1]	178	[2]
Total liabilities	1,144,512	[1]	1,047,357	[2]
Stockholders' equity:
Additional paid-in capital	26,271	[1]	26,271	[2]
Accumulated other comprehensive loss	32,310	[1]	4,210	[2]
Retained earnings	213,088	[1]	193,722	[2]
Unearned employee stock ownership plan shares	0	[1]	0	[2]
Total stockholders' equity	274,169	[1]	226,703	[2]
Total liabilities and stockholders' equity	1,418,681	[1]	1,274,060	[2]
Operating Segments [Member] | Life Insurance [Member] | Rental Trailers and Other Rental Equipment [Member]
Property, plant and equipment, at cost:
Property subject to or available for operating lease, gross	0	[1]	0	[2]
Operating Segments [Member] | Life Insurance [Member] | Rental Trucks [Member]
Property, plant and equipment, at cost:
Property subject to or available for operating lease, gross	0	[1]	0	[2]
Operating Segments [Member] | Life Insurance [Member] | Series A Preferred Stock [Member]
Stockholders' equity:
Preferred stock, value, issued		[1]		[2]
Operating Segments [Member] | Life Insurance [Member] | Series B Preferred Stock [Member]
Stockholders' equity:
Preferred stock, value, issued		[1]		[2]
Operating Segments [Member] | Life Insurance [Member] | Series A Common Stock [Member]
Stockholders' equity:
Common stock, value, issued		[1]		[2]
Operating Segments [Member] | Life Insurance [Member] | Amerco Common Stock [Member]
Stockholders' equity:
Common stock, value, issued	2,500	[1]	2,500	[2]
Operating Segments [Member] | Life Insurance [Member] | Common Stock in Treasury [Member]
Stockholders' equity:
Treasury stock, value	0	[1]	0	[2]
Operating Segments [Member] | Life Insurance [Member] | Preferred Stock in Treasury [Member]
Stockholders' equity:
Treasury stock, value	0	[1]	0	[2]
Eliminations [Member]
ASSETS:
Cash and cash equivalents	0		0		0		0
Reinsurance recoverables and trade receivables, net	0		0
Inventories, net	0		0
Prepaid expenses	0		0
Investments, fixed maturities and marketable equities	0		0
Investments, other	0		0
Deferred policy acquisition costs, net	0		0
Other assets	0		0
Related party assets	(16,104)	[5]	(16,409)	[5]
Subtotal assets	(16,104)		(16,409)
Investments in subsidiaries	(443,462)	[6]	(373,490)	[6]
Property, plant and equipment, at cost:
Land	0		0
Buildings and improvements	0		0
Furniture and equipment	0		0
Property, plant and equipment (gross)	0		0
Less: Accumulated depreciation	0		0
Total property, plant and equipment	0		0
Total assets	(459,566)		(389,899)
Liabilities:
Accounts payable and accrued expenses	0		0
Notes, loans and leases payable	0		0
Policy benefits and losses, claims and loss expenses payable	0		0
Liabilities from investment contracts	0		0
Other policyholders' funds and liabilities	0		0
Deferred income	0		0
Deferred income taxes, net	0		0
Related party liabilities	(16,104)	[5]	(16,409)	[5]
Total liabilities	(16,104)		(16,409)
Stockholders' equity:
Additional paid-in capital	(117,601)	[6]	(117,601)	[6]
Accumulated other comprehensive loss	(41,181)	[6]	(5,992)	[6]
Retained earnings	(278,879)	[6]	(244,096)	[6]
Unearned employee stock ownership plan shares	0		0
Total stockholders' equity	(443,462)		(373,490)
Total liabilities and stockholders' equity	(459,566)		(389,899)
Eliminations [Member] | Rental Trailers and Other Rental Equipment [Member]
Property, plant and equipment, at cost:
Property subject to or available for operating lease, gross	0		0
Eliminations [Member] | Rental Trucks [Member]
Property, plant and equipment, at cost:
Property subject to or available for operating lease, gross	0		0
Eliminations [Member] | Series A Preferred Stock [Member]
Stockholders' equity:
Preferred stock, value, issued
Eliminations [Member] | Series B Preferred Stock [Member]
Stockholders' equity:
Preferred stock, value, issued
Eliminations [Member] | Series A Common Stock [Member]
Stockholders' equity:
Common stock, value, issued
Eliminations [Member] | Amerco Common Stock [Member]
Stockholders' equity:
Common stock, value, issued	(5,801)	[6]	(5,801)	[6]
Eliminations [Member] | Common Stock in Treasury [Member]
Stockholders' equity:
Treasury stock, value	0		0
Eliminations [Member] | Preferred Stock in Treasury [Member]
Stockholders' equity:
Treasury stock, value	$ 0		$ 0

[1] Balances as of December 31, 2014

[2] Balances as of December 31, 2013

[3] Balance for the period ended December 31, 2013

[4] Balance for the period ended December 31, 2012

[5] Eliminate intercompany receivables and payables

[6] Eliminate investment in subsidiaries